A base plate (1) for a plate compactor has a first surface (2) for use in initial compaction of material and a second surface (3) depending therefrom for final compaction of the material. The projected area of the second surface (3) is not more than substantially half of the projected area of the first surface (2).
The present invention relates to a base plate for a plate compactor and a compactor provided with such a base plate.
Known plate compactors have a flat base plate, which is usually curved in an upwards direction at both ends to allow the compactor to ride over small obstacles such as stones.
The heavier the plate compactor, the more likely it is to become buried when compacting soft ground. This tends to occur when the compactor is driven by a heavy diesel engine. In order to overcome this problem it is known to increase the area of the base plate. However, this reduces the static weight of the plate compactor per unit area of the plate, and therefore the dynamic force per unit area, thus reducing the degree of compaction.
An object of the present invention is to provide a base plate for a plate compactor by means of which the static and dynamic force per unit area can be increased without the base plate sinking into softer ground.
The invention provides a base plate for a plate compactor having a first surface for use in initial compaction of material and a second surface depending therefrom for final compaction of the material, characterised in that the projected area of the second surface is not more than substantially half of the projected area of the first surface.
Preferably, the projected area of the second surface is not more than substantially one third of the projected area of the first surface.
The second surface may be stepped downwardly relative to the first surface. Alternatively, the first surface may be inclined and/or curved upwardly from the second surface.
Thus, when performing initial compaction on softer ground both the first and second surfaces are used, thereby minimizing the risk of sinking of the compactor. During final compaction, only the second surface is used, thus providing an increased static and dynamic force per unit area. In this way, it is possible to achieve a static weight per unit area of the compactor of 1400 - 1800 kg/m² without necessitating the use of small plates which bog down or very heavy compactors which are difficult to manoeuvre and control. Furthermore, it is possible to define with mathematical precision the applied static and dynamic forces per unit area which was hitherto difficult to achieve.
Embodiments of the invention will now be described with reference to the accompanying drawings, wherein:
In Figures 1 to 4 a compactor base plate 1 has a first surface 2 and a second surface 3 depending therefrom via a step 4. The area of the second surface 3 is approximately one third of the area of the first surface 2 which, for the avoidance of doubt, includes the area of the second surface 3. The area of the second surface 3 could however be as much as substantially one half of the area of the first surface 2. The area of the second surface 3 is such that, when the entire weight of the compactor is supported thereon, the static weight per unit area is at least 1400 kg/m².
In Figure 3 the base plate is shown during initial compaction of soft ground in which both the first surface 2 and the second surface 3 take part in compaction. As the compacted ground becomes harder, the first surface 2 becomes less and less effective until compaction is performed solely by the second surface 3 providing an increased static and dynamic force per unit area than for the surfaces 2 and 3 together.
As shown in Figure 2, the second surface 3 extends laterally up to one side 5 of the base plate 1 so that the base plate can be used to provide final compaction up to an edge, e.g. to a kerb. If desired, the second surface 3 can be extended laterally up to the opposite edge 5' of the base plate 1 so that compaction can be performed up to opposite kerbs without turning the compactor round.
Figure 5 shows an alternative base plate in which the first surface 2 is curved downwardly to meet the second surface 3, and Figure 6 shows an alternative base plate in which the first surface 2 is inclined downwardly towards the base plate 1.
Figure 7 shows the base plate of Figure 5 during initial compaction and Figure 8 shows the base plate of Figure 6 during final compaction.
The second surface 3 need not necessarily be a single continous surface. It could, for example, be formed as two or more separated surface portions 3', 3'', as shown in Figures 9A and 9B.