Patent Application
20230028817
The present invention relates to a saw for forming a trench in the ground for laying cables in, and a method of forming such a trench.
Various types of electrical and data transmission cables are required to be laid underground. Examples of such cables include fibre-optic cables for high-speed transmission of data. Placement of such cables underground can significantly improve their reliability and impact on the environment, when compared with running the cables by the use of pylons, for example. Pylons and other forms of fixed structures to assist overground positioning of cables are susceptible to damage in severe weather, and are unsightly. The reliability of underground cables greatly depends on their proper installation. The installation process often involves disruption to transport infrastructure and causes inconvenience to people in the vicinity of the cable installation. Furthermore, the installation process absorbs a significant proportion of the budget for a cable installation project, as the manual work involved in digging and filling the trench is significant with respect to the time and equipment required to lay the cable within the trench.
Typically, a trench is formed in concrete or tarmac by engagement of a road saw with the ground. Typical road saws have a single blade, and an operator must make two separate passes with the road saw to for the trench. It is known to provide a road saw with two circular saw blades which are spaced apart within a safety enclosure forming a guard around the circular saw blades. As a brief overview of the trench digging operation, the operator aligns the road saw and starts the engine to drive the shaft to which the circular saw blades are attached. The road saw is moved along a path to cut a trench. There are various materials which can be used to fill the trench, however it is common for the cables to be installed in a bed of sand. The bed of sand is typically then covered with one or more layers of type 1 backfill and a base layer, and then a layer of tarmac or asphalt on top of the cement. The backfill material is typically placed in layers of 150 mm depth. The top layer, hereinafter referred to as the surface layer, may require compaction by vibrating plate and roller. During backfill, the layers of backfill material may require compaction by a rammer. The rammer is used to compress the aggregate material, increasing the density of said material and ensuring that post laying settlement does not occur. There are several problems with the known equipment and methods for trench construction and completion. Standard single blade road saws require at least two passes of the road saw to cut a trench, and the cutting lines must be accurately marked to ensure an even trench width. Furthermore, prior art twin blade road saws are limited in the width of trench they can cut. This limitation comes from the requirement that the road saw remains portable and light enough to be carried/lifted by the operator. There are therefore design limitations on the weight of the materials. This problem is compounded by the fact that road saws are typically driven be a horizontal drive shaft, with the drive shaft extending from a bearing and carrying the two circular saw blades in a cantilever fashion. The horizontal spacing of the two circular saw blades is limited by the bending moment created by a heavy blade, and associated bearings, spacers etc., being positioned distant from the drive mechanism. Moreover conventional rammers require a large base plate, with a footprint having a width which does not fit within the trench formed by a prior art twin blade road saw, so that the backfill material in such a trench cannot be compacted properly.
If a wider trench is to be cut, then the usual practice is to use a single blade road saw. However such trenches may have an uneven width, and may be substantially greater than the width of the footprint of a base plate. a Because of the aforementioned disruption to the public/transport infrastructure, and the fact that operators are often paid for the job rather than their time, there is a tendency to avoid making two passes with the rammer if possible. However this leads to a poor quality compaction of the trench, thus leading to the aforementioned problems.
It is an object of the present invention to provide a blade drive shaft, and a road saw comprising this blade drive shaft, which overcome at least one of the aforementioned problems. It is a further object of the present invention to provide a method of forming, filling and compacting a trench which overcomes at least one of the aforementioned problems.
According to a first aspect of the invention there is provided a blade drive shaft assembly for a road saw. The blade drive shaft comprises a shaft, a first mounting plate, a spacer removably fitted on the shaft, a second mounting plate removably fitted on the shaft, a mounting plate fixing adapted to secure the second mounting plate to the shaft, a first circular saw blade mounted between the first mounting plate and the spacer, and a second circular saw blade mounted between the second mounting plate and the spacer, wherein the first mounting plate is integrally formed with the shaft from a single piece of metal. This assembly has the benefit of being strong and light. The integrally formed first mounting plate provides strength compared to a first mounting plate welded to a blade drive shaft.
Preferably, the shaft has a diameter greater than 25 mm, and more preferably a diameter of between 26 mm and 35 mm. The strength provided by the integrally formed first mounting plate and blade drive shaft can be utilised to allow the assembly to carry additional weight and bending moment. In this regard, the blade drive shaft can be increased in diameter to further increase the strength of the assembly.
Preferably, the blade drive shaft and the first mounting plate comprise EN19 hardened steel, which is a strong material and is readily available. Furthermore, the material provides a good compromise between weight and strength, which makes it particularly suitable for the portable equipment which must be lifted by a single operator.
According to a second aspect of the invention there is also provided a road saw for cutting a trench in a road. The road saw comprises a road saw body; an engine mounted to the road saw body; a blade drive shaft assembly according to the first aspect rotatably supported by a bearing mounted to the road saw body; a transmission means driveably coupling the engine and the shaft; wherein the first mounting plate, the spacer, the second mounting plate and the first and second circular saw blades are provided on a portion of the shaft cantilevered from the bearing, wherein the first and second blades are arranged 200 mm apart. The road saw provided has improved strength which allows the road saw to carry circular saw blades which are separated by a greater separation than was previously possible, and can therefore cut a trench of larger width than was previously possible. The road saw body provides support such that the blade drive shaft can be carried and operated by the user. The engine, bearing and transmission means provide a driving mechanism such that the blade drive shaft can be driven with the required torque and power.
The spacer axial length provides the separation between the first and second circular saw blades, which provides that the trench cut will be of a greater width than previously possible and can be cut in one cutting operation. There are multiple benefits to a wider trench in one cutting operation. Firstly, a wide trench cut in one pass saves time which saves costs and disruption to the public and infrastructure in the vicinity of the operation, and secondly, a wider trench which is subsequently filled with aggregate material ensures that the operator must make two passes with a rammer to compact the aggregate material, thus providing a better quality fill.
Optionally, the road saw may comprise an adapter for use in conjunction with the spacer, and for providing additional separation between the first and second circular saw blades. This allows the blade separation to be easily adjusted for particular jobs and requirements. This saves the cost of the construction company owning or renting multiple road saws of different blade separations, and allows one road saw to be sent to a job which requires trenches of different widths to be cut.
According to a third aspect of the invention there is provided a method of forming, filling and compacting a trench comprising the steps of: providing a road saw of the second aspect; cutting a trench having a width of at least 200 mm using said road saw; at least partially filling said trench with aggregate material; and compacting a total portion of said aggregate material by passing over the aggregate material with a rammer comprising a footprint with a width less than the width of the trench. This ensures that not all of the aggregate material is compacted as the rammer is passed over the trench. This provides the benefit that the operator must make a second pass to compact the aggregate material left uncompacted after the first pass. This provides a better quality fill of the trench. In this regard it is preferable that the width of the footprint may be at least 30 mm less than the width of the trench, thus ensuring that a visible area of uncompacted aggregate material is left after the first pass, therefore ensuring that the operator must make a second pass.
Preferably the road saw is a road saw according to the second aspect.
Preferably, the step of compacting a total portion of said aggregate material comprises the steps of: compacting a first portion of the total portion with the rammer in a first pass; and compacting a second portion of the total portion with the rammer in a second pass; wherein the first and second portions at least partially cover the same area of aggregate material in a third portion. The third portion which comprises part of the first and second portions may be compacted in the first pass and the second pass. This ensures that the overlapping third portion is compacted with the rammer at least twice, which provides a high quality fill in this portion of the trench.
Optionally, the steps of compacting the first portion and compacting the second portion may together complete the compaction of all of the aggregate material in the trench. This provides that the method cuts, fills and compacts an entire trench, leading to the completion of the job with a high quality fill of the trench.
According to a fourth aspect of the invention, there is provided a method of forming a blade drive shaft for a road saw, comprising the steps of providing a block of raw material and milling the raw material to provide a shaft and an integral first mounting plate. This provides a strong blade drive shaft which can carry increased weight and bending moments, thus allowing for an increased diameter of shaft to be used which further increases the strength of the shaft and allows road saw blades to be positioned further apart on said blade drive shaft.
Preferably, the raw material may be EN19 steel. This is a strong material and is readily available. Furthermore, the material provides a good compromise between weight and strength, which makes it particularly suitable for a drive shaft for the portable equipment which must be lifted by a single operator. Additionally, the material can be hardened after being milled. In this regard, it is preferable that the method may further comprise the step of hardening the blade drive shaft, thus further improving its properties for application in a road saw. Preferably the blade drive shaft so formed is used in the method of making a blade drive shaft assembly according to the first aspect.
Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:
Referring now to
Referring now to
The bush 114b that sits within the pulley member 115b has an internal bore of around 25.4 mm to allow passage of the blade drive shaft 120 therethrough, and may further comprise an internal surface feature which is registered to mate with a feature of the blade drive shaft 120 to allow the bush 114b to engage with the blade drive shaft 120 to turn the blade drive shaft 120. Typically, the pulley member 115b has an external diameter of around 85 mm, and an axial length of around 85 mm. It will be understood that this is just one of a plurality of possible transmission means which can be used to drive the drive shaft.
Referring now to
The standard order of assembly of some of the components is now described, still with reference to
Typically, the blade drive shaft 120 is 25 mm in diameter and around 598 mm in length. A blade guard 101 of around 167 mm in width is typically used with a blade drive shaft of 598 mm. The first mounting plate 125 (which is welded to the blade drive shaft 120) has an outer diameter of around 65 mm. The spacer 126 has an internal bore of 25.4 mm diameter, through its longitudinal axis. The spacer 126 has an outer diameter of around 98 mm at each end, adjacent the first circular saw blade and second circular saw blade. This large outer diameter is require to steady and support the first and second circular saw blade. The spacer 126 may have a reduced outer diameter through the centre of the spacer 126 where no support of the circular saw blades is required, thus reducing the weight of the spacer 126 and overall weight of the saw 100. The spacer 126 has an axial length of around 100 mm, thus the first and second circular saw blades are spaced apart around 100 mm. The second mounting plate 127 has an outer diameter of around 65 mm and an internal bore of 25.4 mm. The bearing assemblies 121, 122 have an internal bore of 25.4 mm to also allow the blade drive shaft 120 to pass therethrough.
Referring now to
The blade drive shaft 220 is further configured for improved strength by means of an increased diameter of 30 mm. This provides a stronger shaft which can withstand higher loads and carry additional weight and/or additional bending moments. This provides an advantage over lower diameter shafts by providing the option of positioning the second circular saw blade further away from the first circular saw blade, as the blade drive shaft 220 can now carry the additional weight and bending moment created by the further away second circular saw blade.
In this regard, the other components located in the protruding region A are also adapted to receive the increased diameter blade drive shaft 220. The spacer 226 has an internal bore of 30.4 mm diameter, through its longitudinal axis. The spacer 226 has an outer diameter of around 100 mm at each end, adjacent the first circular saw blade and second circular saw blade. The spacer 226 has an axial length of around 200 mm, thus spacing the first and second circular saw blades 200 mm apart. This increased spacing can be achieved by the aforementioned increased blade drive shaft 220 diameter, and the stronger integrally formed first mounting plate 225. As previously described, the arrangement transfers large loads to the first mounting plate 225 as the first and second circular saw blades, second mounting plate 227 and spacer 226 are all biased against the first mounting plate 225 by the nut 229. The stronger integrally formed first mounting plate 225 therefore allows the axial length of the spacer 226 to be increased, and the resulting spacing of the first and second circular saw blades to be increased. The second mounting plate 227 is configured to have an increased outer diameter of around 92 mm and an increased internal bore of 30.4 mm to accommodate the increased blade drive shaft 226 diameter.
As a result of the increased load capabilities, the blade drive shaft 220 has an increased length of around 698 mm, allowing for the increased spacer 226 axial length. The length of the blade drive shaft 220 may be increased further to accommodate greater blade separation. In this regard, the spacer 226 may also be increased in axial length, or additional spacers may be added in the form of adapters to increase the separation of the circular saw blades. Different sizes of adapters may be configured to be compatible with the blade drive shaft and associated components of protruding region A. In this regard, a road saw 200 may be provided with a plurality of varying axial length adapters, such that the operator of the blade saw can select the appropriate adapter or adapters for the desired trench width. This allows the road saw 200 to be quickly and easily adapted, and allows for one road saw 200 to be used to cut a plurality of trench widths, rather than requiring many different road saws for different widths. A blade guard of around 267 mm in width is typically used with a blade drive shaft of 698 mm. The blade guard may be further configured with two guide indicators on the outside of the blade guard, i.e. on the side, and located at a position, such that the indicators are visible to the operator when in use. The guide indicators (not shown) may be moveable across the width of the blade guard, such that each indicator can be positioned to indicate the position of the respective blade to the operator. This allows the operator to be certain of the position of the blade when performing the trench cutting operation. This is particularly useful when adapters, or non-standard length spacers, are used to increase or decrease the separation of the circular saw blades from the separation the operator is familiar with.
As previously discussed, the prior art first mounting plate 125 is welded onto the blade drive shaft 125. This provides a weak point in the machine when in use. Milling of material is common in some heavy industries to provide strong components, however it has major drawbacks in terms of energy requirements and time required to form the components. These drawbacks are particularly prevalent when forming low volume components from high volume blocks of raw material. Milling an integral first mounting plate 225 and blade drive shaft 220 from a single block of raw material has shown in this application to outweigh the drawbacks of energy requirements and time, due to the extremely strong blade drive shaft with integral first mounting plate which is formed from the milling operation.
As the length of the blade drive shaft 220 is around 698 mm, and the diameter of the integral first mounting plate 225 is around 92 mm, milling is performed from a rectangular block of raw material with a width of at least 92 mm, a height of at least 92 mm and a length of at least 698 mm.
The above mentioned road saw 200 can be used to cut trenches which are 200 mm wide. In fact, if the blades are 7 mm thick, and the spacer 226 is 200 mm long, the actual width of the trench is 214 mm, or about 220 mm. It is to be understood that a trench width W can refer to an actual width which may be up to W+20 mm. Typically, as shown above, the largest trench width with a standard road saw 100 is around 100 mm. It is highly desirable to cut a larger trench width than the footprint of rammer available, or deployed to the site where the trench is to be cut and filled. The provision of a smaller rammer footprint than trench ensures that the personnel carrying out the compaction with the rammer must pass over the trench twice to compact all of the aggregate material. This would not be required if the trench is the same width as the rammer. For this reason, a wide road saw and standard rammer is highly desirable.
A road saw 200 with the adaptations mentioned above can be used in a method of forming and filling a trench with a width greater than 165 mm, and preferably around 200 mm, using at least two passes of a standard width rammer.
This method is described with reference to
In this regard, the operator is forced to make a second pass, even though only a relatively small portion of the aggregate material has not been compacted. This provides the advantage of ensuring that a second pass is always made, which provides better overall compaction of the aggregate material when compared with a single pass.
Referring now to
The rammer 602 used in the method has a footprint with a width smaller than the width of the trench 600. Some of the largest common rammer footprint widths available are around 165 mm, thus using a standard footprint rammer with a trench greater than 165 mm wide, such as around 200 mm wide, forces the operator to make two passes, and provide compaction twice to a large proportion of the surface area of the trench. This method overcomes the aforementioned issues in the construction industry relating the operators having a tendency to avoid a second pass with the rammer where possible, thus leading to a higher quality fill of a trench.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1918542.0 | Dec 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2020/053245 | 12/16/2020 | WO |
