Description The invention pertains to a device for smoothing freshly cast concrete surfaces, which device has at least two trowels mounted on corresponding extremities of rotatable axles, which axles are connected to an engine via a driving mechanism and a clutch connected to the driving mechanism. Such a device for smoothing relatively large freshly cast concrete surfaces by hand has already been on the market for a considerable time. A known device which, in addition to interlocking or non-interlocking rotatable trowels, is also furnished with a seat and with control means for tilting the rotatable axles, and thus steering the device, is eminently suited to making large, freshly cast concrete surfaces almost perfectly smooth, in a very short time.

The problem associated with working with the known device, however, is that it cannot be used for good, sufficiently accurate work at the sides and along the edges of the cast concrete surface. In particular, the finish along walls and around pillars leaves a lot to be desired.

Often, the edges require supplementary filling, evening and smoothing by hand, because the known device cannot get into cor- ners or sufficiently close to edges. In particular, a difficult situation can arise whereby finishing the edges of the cast concrete surface requires so much time that, under certain circumstances, that part of the surface which was last cast can have hardened to such an extent that (in particular) the unfinished top layer along the edges can only be smoothed out with difficulty using hand tools, and the toplayer can have set to such a degree that it cannot be completely smoothed out without adding some water. Between one thing and another, so much extra effort and time are required that these factors significantly influence the cost price per unit area of the surface.

The aim of the invention is the provision of a device with which it is possible to rapidly finish and completely smooth the

edges while the freshly cast concrete is still setting, without necessitating input of extra manpower.

To this end, the device according to the invention is char¬ acterised in that the device possesses a frame which can be displaced by hand along (in particular) obstacles in the cast concrete surface, with the characteristic that the frame is constructed from a box-like body with a sump base and a sump lid, to which bearing means and part of the axles ¹ driving mechanism are attached, whereby a driving shaft from the driving mechanism protrudes through the sump lid, whereby the driving mechanism is embodied with wheels attached to the rotatable axles, whereby the extremities of the rotatable axles protrude through the sump base, and whereby the working surfaces of the trowels are partly flush with the circumferential edge of the box-like body.

Because the device according to the invention enables rapid finishing of (in particular) the edges, the same person who operates the device according to the invention in finishing the edges after the entire concrete surface has been cast can now be assigned to further finish the incompletely set concrete in the remainder of the large surface using the known device for smoothing larger concrete surfaces, whereby any imprints present in the cast concrete near the edges will be automatically removed. Application of the device according to the invention also allows several persons to work simultaneously so as to finish the floor in a single unbroken run, which has proved impossible up to now.

The saving in labour and time which results from application of the device according to the invention is thus, in general, very substantial. This is because the various procedures involved in finishing the concrete surface are in fact comprised of sub- procedures, in the first of which the solid constituents of the fresh concrete, such as stones, are suppressed, after which the smoothed surface is allowed to harden for some time, after which, in the next sub-procedure, the somewhat hardened top layer is smoothed so as to remove the smaller imperfections and cavities, after which the top layer is further allowed to harden. The relevant sub-procedures are repeatedly performed until a truly

polished surface has been obtained.

It is preferable if the device according to the invention is thus embodied that the rotatable axles are positioned at mutually equal distances. This preferential embodiment of the device according to the invention has the advantage that symmetric placement contributes to a uniform distribution of weight, so that a uniform amount of effort is required for movement by hand of the device according to the invention in the various desired directions, thus advantageously influencing comfort of control.

It is particularly preferable if a practical, easily control¬ lable and easy-to-manufacture embodiment of the device according to the invention is characterised in that it possesses three trowels with corresponding rotatable axles which are located on the bisector of the corner-points of a triangular plate, whereby the sump lid is provided with a flange within which moves the driving shaft, which is positioned so as to be an extension of one of the rotatable axles, on which flange are located a transmission, with a clutch (preferably automatic) which is switched in above a stationary angular velocity, and an internal combustion motor (preferably single-cylinder) .

The invention and its further advantages are further eluci¬ dated with the aid of the accompanying figures, in which similar elements are provided with corresponding reference numbers. The content of the figures is as follows: figure 1 renders a plan of the frame of the device according to the invention, in which the position of various elements can be seen; and figure 2 is a combined rendition, whose upper part depicts a view of the device according to the invention and whose lower part shows a cross-section along the line 1-1 of the rendition of the device in figure 1.

Figure 1 shows a plan of a frame 1 of a device 2 for smoothing freshly cast concrete surfaces. The device 2 is shown in figure 2, whereby the lower part of this figure is a cross-section along the line 1-1 in figure 1 and the upper part is a view. The frame 1 is constructed from a box-like body with a sump base 3 and a

sump lid 4. Parallel axles 5, 6, 7 are mounted in bearing means 8 in the the box-like body. The bearing means 8 are mounted now and again around each of the axles 5, 6, 7 and against the respective insides of the sump base 3 and the sump lid 4. The depicted bearing means are embodied as ball bearings. The axles 5, 6, 7, which are mounted in bearing means and are rotatable in the box¬ like body, are provided with respective driving wheels 9, 10, 11, around which a driving belt is slung. The driving mechanism in the form of the driving wheels 9, 10, 11 and the driving belt 12, all mounted in the box-like body, is preferably embodied with cogs, in which case the driving belt 12 is provided with teeth on at least one side.

Figure 2 shows that, between the axles 5 and 6, a tensioning roller 13 in the box-like body is attached to a belt tensioning device 14. The extremities of the axles 5, 6, 7 protrude on one side through the sump base 3, and trowels 15 are fixed on this same side of the respective axles. The trowels 15 have a saucer- shaped external surface 16, which can possess spherical curvature (not depicted) . The external surface 16 is provided with a turned circumferential edge 17.

In the depicted embodiment, a driving shaft 18 is directly coupled to the axle 5, which driving shaft 18 continues on into a flange 19 mounted in the sump lid 4. To the flange 19 is fixed a worm-wheel housing 20, which constitutes part of the driving mechanism for precipitating rotation of the axles 5, 6, 7 and the relevant trowels 15 with which the freshly cast concrete surface can be finished. The worm-wheel housing possesses a transmission ratio which lies somewhere between 1 in 10 and 1 in 20, for example, the actual value depending somewhat on the desired angular velocity of the axles 5, 6, 7. The undepicted incoming axle of the worm-wheel housing 20 is coupled to an automatic clutch 21, which, if so desired, can be coupled to a reduction mechanism, with a transmission ratio of 1 in 4, for example. In the depicted embodiment, the clutch 21 is coupled to an internal combustion engine 22, which, in general, will be a single- cylinder internal combustion engine. The automatic clutch is embodied as a centrifugal clutch in such a way that, above a certain minimal, stationary angular velocity of the internal

combustion engine 22, the clutch 21 will switch in automatically, whereby the trowels 15 are set in motion. The advantage of this is that the device 2 becomes simple, since means such as a Bowden cable and a handle are not required to operate the clutch. In the depicted embodiment, a handle 23 is fixed to the worm- wheel housing 20. The handle 23 extends along the perpendicular bisecting plane between the axles 6 and 7, and makes it possible, by allowing slight tilt of the frame 1, to allow the device 2 to move in each desired direction. In the event that each of the trowels 15 is rotating in the same' direction, such as clockwise rotation as viewed in figure 1, then, upon suitable exertion of force on the handle 23, whereby, for example, a larger force is exerted on the trowel 15 of the axle 6 than on the trowel of the axle 7, the device 2 will move to the left, along a line which passes through the axle 6 and the axle 5. If such a force is exerted that its effect on the trowel 15 of the axle 7 is larger than on the trowel 15 of the axle 6, then the device 2 will move to the bottom right, along a line which runs from the axle 5 to the axle 7. In this way, the device 2 can be moved in a very easy and very accurate manner alongside obstacles in the freshly cast concrete surface.

The construction of the device 2 is such that the worm-wheel housing 20, the clutch 21 and the engine 22 lie in-line and close to the sump lid 4, whereby the centre of gravity of the device 2 is not only low, but is also almost centred on the triangular sump lid, which fact, in combination with the discussed specific orientation of the handle 23, leads to a device 2 which can be even better manipulated around local obstacles. The horizontally- running engine shaft (not depicted) runs via the clutch 21 to the worm-wheel housing 20, where the motion is transmitted, under an angle of 90 degrees, to the vertical driving shaft 18 in the flange 19.

Mounted along the circumference of the sump base 3 is a circumferential edge 24, which runs flush with the circumfe- rential edge 17 mounted on the external circumference of the external surface 16, as indicated by a broken line. In this manner it is ensured that, if the circumferential edge 24 meets an obstacle, the freshly cast surface will only be finished and

smoothed as far as the foot of this obstacle.

After a preliminary smoothing sub-procedure with the trowels 15 having a somewhat saucer-shaped external surface 16, it is preferable to screw-mount a second set of trowels onto the threaded axles 5, 6, and 7, each of which is provided with undepicted sprung plates. So doing, it becomes possible to finish the top layer of the somewhat hardened freshly cast concrete surface in such a way that this is effectively polished flat in the second finishing phase. The wear-resistant sprung rectangular plates, of which, for example, three of four are mounted in a radial orientation on the external surface of the trowel, have corner-points which are rounded in such a manner that they do not cut into or leave grooves in the concrete during subsequent finishing of the concrete surface. To this end, the sprung plates are fixed to the external surface of the trowel at a small angle with respect to this external surface.