ASSEMBLY COMPRISING SAID SUPPORT

DESCRIPTION:

The present invention relates to a working assembly for sanders. In particular, the invention relates to a support for flexible abrasive elements to be applied to these sanders. More particularly, these supports move with a rotary-orbital movement, suitable for sanders for flat surfaces.

The machines to which the present invention relates are used to smooth surfaces made of, for example, wood, stone, etc., and more specifically for wooden floors, such as parquet floors.

As is known, smoothing wooden (parquet) floors is a task carried out for the first time after the floorboards have been laid, and possible also later, in order to maintain and floor and restore the original appearance thereof in cases where it is worn and/or damaged. The task consists of the removal of a layer of material, specifically wood and any paint or coatings applied thereto, with a thickness that can vary from a few tenths of a millimetre to a millimetre or more, in order to obtain a perfectly flat surface free from rough edges or grooves.

This operation is performed using special sanders. Some types of machines use an abrasive strip mounted around a horizontal roller that rotates in contact with the floor surface. These machines, however, are not suitable for sanding the perimeter areas of the floor, i.e. those areas next to walls and/or skirting boards.

Other types of machines commonly used for sanding wooden floors are rotary -orbital type machines.

In rotary-orbital type sanders, each working assembly comprises a working element, which constitutes the actual sanding part of the sander, typically in the form of a flexible abrasive disc made of paper or polymer, and a support, or so-called backing pad. Typically, the working element is removable, meaning that it is fixed to the supporting element by temporary connecting means (tear-off, adhesives, or similar) so that it can be replaced by new elements and/or elements of a different type, re-using the same support.

Said support has a face, hereafter referred to as the coupling face, to which said working element is made to adhere, and a second face, hereafter referred to as the upper face, which connects by means of appropriate connecting means with the body of the sander.

More specifically, in known working assemblies such as described above, both the working element and the support are circular in shape with flat bases, so that both the coupling face, which is flat, and the working element are substantially parallel to the flat surface to be treated.

Said rotating support can be a simple or compound type, depending on the number - one or more - of essential components of which it is formed.

With reference to sanders with a known composite support, the support comprises two discoid components, overlapping and coupled to one another, which differ in terms of the type and properties of the material from which they are formed. In particular, one is a rigid body and the other is a layer of deformable elastic material, typically an expanded polymer. To this layer is fixed the flexible abrasive element, the working surface of which remains flat and parallel to the flat surface to be treated. In these supports, since the rigid body and flexible element are overlying and coupled, a face of one component is in contact with a face of the adjacent component. These faces are hereinafter referred to as intermediate faces.

These know supports have the drawback of exerting a non-homogeneous sanding action on the treated surface. Indeed, following the passage of sanders fitted with said supports, some portions of the floor surface remain visibly less sanded than other areas of the floor treated in the same manner. This reduced sanding effect occurs where the contact pressure exerted by the machine on the surface areas to be treated is less than in those surface areas where the contact pressure is greater. These portions of the floor are, typically, at the outer edge of the abrasive working element. When sanding indoor floors, this effect is manifested in the form of reduced sanding action, or removal, in areas near walls or other vertical surfaces, such as items of furniture, etc.

A further drawback encountered with said known supports are the strong vibrations generated by the relative movement between the abrasive element and the surface to be sanded, vibrations that, in addition to causing a constant variation in pressure, and thus reduced sanding precision, also reduce the comfort of the operator using the machine.

In this context, the object of the present invention is to eliminate the aforementioned drawbacks caused by known composite supports.

In particular, an object of the present invention is to provide a support for a flexible abrasive that, during use, makes it possible to have a distribution of pressure on the working surface enabling homogeneous sanding from the centre to the edge of the flexible abrasive element.

These drawbacks are overcome, or at least reduced, by a composite support such as those known supports described above, in which, however, at least one of the two said overlying and coupled components, i.e. the rigid body and the elastically deformable layer, is hollow.

This configuration for the composite support makes it possible to distribute the pressure of the sander in a graduated manner over the entire working surface of the flexible abrasive element, and in particular being greater at the edge and less at the centre of the support, so that each part of the flexible abrasive element can work with the same force as the part next to it. The result for the sanding is a more constant and uniform removal of material over all of the treated surface.

This and other objects are achieved by a support, having a substantially circular shape, comprising at least one flexible layer of elastically deformable material and a rigid body. The latter component is overlaid the flexible layer. More precisely, the lower face of said rigid body is in contact with an upper face of said flexible layer. The latter is adapted to be coupled, typically in a releasable manner, with a flexible abrasive element.

In the support according to the present invention, said coupled faces of the rigid body and the flexible layer have complementary shapes. Furthermore, a face of at least one of said two components has an inward-curved face, forming a downward-facing cavity. Additionally, at least said flexible layer has a thickness that varies homogeneously from the centre towards the outer edge.

Preferably, both the rigid body and the flexible layer are generally circular in shape.

According to a first embodiment, the support has a lower face, i.e. the face coupling with the flexible abrasive element, that is hollow or inward-curved. In particular, only the flexible layer has said hollow or inward-curved lower face, while the coupled faces are substantially flat and parallel. According to this embodiment, the flexible layer has a thickness that is minimum at the centre and maximum at its outer edge. Typically, on the other hand, the rigid body has a constant thickness and, preferably, has a circular or disc-like shape.

In a second embodiment, the support has a generally cylindrical shape, with its lower surface, i.e. the surface for coupling with the flexible abrasive element, flat. In this variant, it is the rigid body that has its lower face, i.e. the intermediate face, inward-curved, so as to form a hollow. The flexible layer is inserted partially and in a complementary manner into this hollow.

In this variant, however, the lower face of the support is completely parallel to the flat surface to be treated.

More specifically, in this variant, the flexible layer has a thickness that varies homogeneously from the centre towards the outer edge and, in particular, it is minimum at the outer edge and maximum at the centre. Possibly, even the thickness of the rigid body can vary homogeneously from the centre towards the outer edge, and is minimum at the centre and maximum at the outer edge.

Both embodiments described enable the proposed objects to be achieved, i.e. to make the sanding or removal action of the flexible abrasive element uniform over the entire surface.

With the first embodiment, indeed, during use the flexible layer is deformed, under the weight of the machine and/or applying an external force, at least until the lower coupling surface, and therefore the flexible abrasive, are completely flat. In this condition, the surface of the flexible abrasive element is substantially fully in contact with the surface to be treated. The increased deformation (crushing) of the flexible layer at the outer area, with respect to the central area, results in a greater elastic response in this area from the material, which presses the abrasive element more against the surface to be treated. The result, as mentioned above, is a more uniform removal of material over the entire surface of the flexible abrasive element.

In the second embodiment, on the other hand, given the flat shape of the lower coupling surface of the flexible layer and thus of the flexible abrasive, the latter is substantially always in contact with the working surface. As a result of pressure applied to the support, due to the weight of the machine and/or an external force, the flexible layer is deformed by crushing to a constant height. However, the differing thickness of the layer means that the percentage of deformation is different at the centre than at the edge, and in particular is greater in the latter area where the layer is thinner. In this case, too, the result is a greater elastic response at the edge area, resulting in increased pressure of the flexible abrasive element against the ground, and therefore uniform sanding over the entire surface.

In the support according to the present invention, the inward-curved face of said components, i.e. the flexible layer or rigid body, may, indifferently, have curved or straight walls. More specifically, the surface of said inward-curved face of the rigid body or of the flexible layer can have a curved or straight generator. As a result, this inward-curved cavity can have a domed, rounded, conical or truncated cone shape.

As a whole, the support typically has a substantially axisymmetric structure.

Preferably, the difference in thickness between the maximum height and the minimum height of the flexible element is between 2 and 4 mm, and more preferably between 2.5 and 3.5 mm.

Preferably, the flexible layer has the following thicknesses:

- a maximum thickness of between 5 and 10 mm, more preferably between 5 and 8 mm, and

- a minimum thickness of between 3 and 5 mm, more preferably between 3.5 and 4.5 mm.

More preferably, the difference between the maximum thickness and the minimum thickness is between 1.5 and 5 mm, and even more preferably between 2 and 4 mm.

In said first embodiment the rigid body, preferably, has a thickness of between 1 and 3 mm, more preferably between 1.5 and 2.5 mm.

In said second embodiment the rigid body, where it is of variable thickness, preferably has a maximum thickness of between 2 and 8 mm, more preferably between 2 and 5 mm.

According to a variant, the rigid body is covered at the side by the flexible layer.

Said support can be connected, on one side, on top, to the remaining part of the sander by known means and methods used for known supports used for the same purpose, which will therefore not be described here in detail. On the other side, on the bottom, the support can be coupled with the flexible abrasive element. According to a variant, the flexible layer can be coupled directly to the flexible abrasive element. The term 'directly' refers to coupling means, such as a tear-off fastening system, or other stable or temporary coupling means of a known type, where there are no layers between the flexible layer and the flexible abrasive element. According to another variant, interposed between the flexible layer and the flexible abrasive element there may be a further layer of various materials, for example a“pad” adapted to dampen further the vibrations generated during operation.

A further object of the present invention is a working assembly that comprises the support as described above and said flexible abrasive element, for example of a known type, such as abrasive paper or similar.

The latter has an abrasive face turned towards the surface to be treated and an upper face adapted to be fixed to the lower face of the support, i.e. its coupling face. This upper face of the abrasive element is coupled with the coupling face of the support. For example, the use of mechanical fastening means is known, such as a tear-off system, which is known to be composed of two parts that can be joined together and then separated, having small hooks on one side and small slots on the other side. Each of said parts of the system is placed on a respective element to be coupled, which in this case is the support and the flexible abrasive element.

In order to fasten the flexible abrasive element onto the coupling face of the support with the tear-off system described above, one of the parts of the tear-off fastening system is present on said coupling face, while the other part is present on the upper face of the flexible abrasive element.

Said type of flexible abrasive element is already known, therefore it will not be further described in detail.

Further features and advantages of the present invention will become more evident from the following description of a preferred, but not exclusive embodiment of a support element as illustrated in the accompanying drawings, wherein:

- figure 1 shows an exploded view of a vertical cross-section of the working assembly for a sander, according to a first embodiment of the present invention;

- figure 2 shows an exploded view of a vertical cross-section of the working assembly according to a second embodiment of the present invention;

- figures 3a, 3b, 4a and 4b shows the results of sanding tests carried out on wooden surfaces.

With reference to figures 1 and 2, the reference numbers 100 and 10 are used to indicate, as a whole, respectively, a working assembly for sanders and the support for a flexible abrasive element, the latter being indicated by the number 5.

In the context of the present invention, the term“centre” should also be taken to refer to the“central zone”. Furthermore, the relative terms, such as upper, lower, and horizontal, refer to the sander, the working assembly, the support, and the abrasive element in their operating positions, which for the working assembly, the support and the abrasive element means oriented with the connecting means facing upwards and the abrasive face of the abrasive element facing downwards, as shown in figures 1-3.

Figures 1 and 2 show two examples of two different embodiments of the support 110 according to the present invention.

In particular, these figures show the flexible layer 3 overlaid by the body 1, showing an upper face in the centre of which there are connecting means 2.

In one embodiment, shown in figure 1, the support 10 is in the form of a cylinder with a hollow bottom. In particular, the rigid body 1 is in the form of a disc and the flexible layer 3 has an inward-curved lower face 3b which forms a cavity with a domes or truncated cone shape.

In this embodiment, the horizontal upper face 3 a of the flexible element 3 couples with the lower face lb of the rigid body 1. The inward-curved face 3b of the flexible element 3 is therefore the face of the support 10 that couples with the flexible abrasive element 5. In this embodiment, the working surface is therefore inward-curved, as shown in figure 1.

In the embodiment shown, the rigid body 1 has a constant thickness of 2 mm and the flexible layer 3 has a thickness of 6 mm at its edge, where the thickness of the layer is maximum, and a thickness of 3 mm at its centre, where the thickness of the layer is minimum.

In a second embodiment (figure 2), the support has a generally cylindrical shape, in which the upper and lower faces of the cylinder are the upper face la of the rigid body 1 and the lower face 3b of the flexible layer 3, respectively. Furthermore, the rigid body 1 has an inward-curved lower face lb, forming a cavity. The protruding upper face 3a of the flexible layer 3 is inserted complementarily into this cavity.

In this variant, the lower face of the support 10, coincident with the lower face 3b of the flexible layer 3, is flat and horizontal. Therefore, the flexible abrasive element 5 fixed to this face 3b also assumes a substantially flat shape. In this embodiment, therefore, the working surface is flat, as shown in figure 3.

In this embodiment, the rigid body 1 has a thickness of 2 at its centre and a thickness of 5 mm at its edge, and the flexible layer 3 has a height of 3 mm at its edge, where the thickness of the layer is minimum, and 6 mm at its centre, where the thickness of the layer is maximum.

The working assembly and, in particular, the support as a whole, as well as its constituent parts, have the same dimensions in terms of diameter and thickness and are produced using any of the known materials usually used for this type of application.

In particular, the support typically has a diameter of between 50 mm and 250 mm.

In the examples shown in figures 1 and 2, the flexible layer has a thickness of between 2 mm and 5 mm, corresponding to the minimum and maximum thicknesses, while the rigid body has a constant thickness of 2 mm.

The flexible layer 3 is made of an elastic material such as expanded polymers or expanded polyurethane. Preferably, the expanded polymers used have a Shore A hardness of between 20 and 25 points.

The rigid body 1 may be made of various materials, such as metal, plastic, or composite materials, for example reinforced polymers. Typically, the rigid body 1 is made of fiberglass.

As mentioned above, the body 1 of the support is connected to the body of the sander by means of connecting means 2. The upper face la of the body 1 has these connecting means 2. An example of a connection is that formed by a hub, present on said upper face la of the body 1, which couples with a driving part of the sander. Naturally, other connecting methods are also possible.

In the examples shown, the flexible abrasive 5 is fixed to the support, and more precisely to the flexible layer 3, by tear-off means, indicated as a whole by the reference number 4. A first part 4a of said tear-off means is in one piece with the lower surface 3b of the flexible layer 3, while the remaining part 4b is in one piece with the flexible abrasive 5.

Figures 3a and 3b show the result of a comparative sanding test carried out using a Flexisand rotary -orbital sander sold by the company Bona AB. The machine was fitted with four rotating heads according to known art, i.e. with a cylindrical support with flat coupling surfaces, more precisely with a Powerdrive support sold by the company Bona AB, with a diameter of 410 mm. The flexible abrasive used, coupled to the support, was by the brand SIA, model 2812 with a grain of 40.

Figures 4a and 4b show the result of a sanding test carried out with the same machine and with the same type of flexible abrasive, but applied to a support according to the first embodiment of the present invention.

In both tests, the wooden floor was sprinkled with a layer of graphite powder to highlight the effect of the sanding. After 1 minute of sanding in both tests, carried out using the two different working assemblies, it can be clearly noted that the sanding carried out using the working machine fitted with the support according to the present invention in the first test completely removed said powdery material in the machine's working area, i.e. right up to the wall, while in the comparative sanding test carried out using the machine equipped according to known art, the sanding is less effective.

This unsatisfactory result, which is evident from the traces of dirt, i.e. graphite, that can be clearly seen next to the vertical wall delimiting the working area, is due to the aforementioned reasons that do not allow the flexible abrasive to reach the entire surface of the area to be sanded and to exert uniform pressure. In these areas the reduced sanding action has failed to completely remove the ridges/veins present on the surface, in which the graphite powder has been trapped and remains visible.

The invention has been described for the purpose of non-limiting illustration, according to several preferred embodiments. Experts in the sector will be able to find numerous other embodiments and variants, all of which fall within the scope of protection of the following claims.