1. Field of Invention
This invention relates generally to improvements in road building machines, and more particularly, but not by way of limitation, to road building machines generally referred to as slipform paving machines.
2. Description of Prior Art
The art of road building has produced many machines designed to form concrete and the like into continuous lanes of finished roads. As highway building programs have progressed, there have been many improvements in machines to pave the large number of miles of roads this country and others have constructed. Primarily, such developments have brought about machines that can be used for highway construction where the goal generally is economy of operation in building acceptible roads at a relatively rapid rate along prepared roadbed surfaces.
Slipform paving machines of prior art design have performed with varying degrees of success toward this goal. Such machines of necessity have often been extremely large and cumbersome, requiring a relatively large amount of time to set up for a given road construction job. When transferring a paving machine from one job site to another, much time and effort must be expended to prepare the machine for transport, and then usually there is need to use several vehicles to transport the machine which has been broken down into several large component parts. Upon arrival at the new job site, the set-up of the machine is repeated wherein a large amount of time and effort must again be expended. Often this process has required several days to complete a break down at the old job site and a set-up at the new job site.
As more and more short run roads have been built, the need has arisen to provide a road building machine that offers versatility of operation so that it can be used on one job site, prepared for transportation, transported to a new job site and set up at the new job site with a minimum expenditure of time and effort. Since it is customary that such machines are transported over the road system which they have helped build, a desirable attribute would be the capability of remaining intact for transporting over road systems and the like that have a maximum allowable width.
Another desirable attribute of a machine to be used on short run roads is that it is capable of use on highway systems as well, and it should be capable of laying down roads varying between the narrow roads of a suburb and the very wide lanes of super highways and the like. That is, the machine should be capable of performing on a large variety of job sites, and not merely on small road systems.
A problem that has been faced in slipform paving machines is the large amount of power required by such machines to literally bulldoze their way through the bulk concrete material that is placed in front of the machine for form working. Slipform paving machines must spread and form the concrete mix by extruding it through pressure plates provided on the top and sides of the concrete, generally using the weight of the machine to provide the force required to form the mix into a finished concrete road. It has been found in practice that the bulk of the concrete mix in front of the machine presents a formidable mass for the machine to confront, spread and work. Further slipform pavers have required massive frameworks in order to provide enough weight as applied to the extrusion plates to work the concrete mix. This has been compounded by the stiffer mixes of concrete that have been developed in recent years, and are presently still developing. To drive these large machines, large power plants have been required and economy of operation has accordingly suffered, and in addition, the quality of road surfaces has often been less than desired. Means reducing power and size requirements of slipform pavers, while improving road quality, have been needed.
In the building of short run roads, such as are often found in housing development areas, a variety of roadbed conditions is often encountered. That is, contrary to the generally spacious roadbeds found in the production of highway systems, short run roads often present the problems of tight space conditions wherein a slipform paving machine must operate in a minimum of space, even to the extremes of placing its wheels or other motive means into ditches or over banks and other obstacle type or surfaces. These conditions have prevented most prior art pavers from being used, although the advantages obtained by their use would have been apparent. Therefore, a slipform paver capable of building paved roads in restricted space conditions and capable of operating over many conditions of terrain has been needed.