Rotating grinding or polishing disc

A rotating grinding or polishing device includes a number of grinding or polishing discs formed of two or more layers of segments radiating from a central retaining area having an edge which defines a central hole. In the central area, the segments are kept together by a heat-activatable string which also maintains the grinding or polishing disc in the form of a ring, whereby the disc has the required optimum stiffness/flexibility for obtaining an effective grinding or polishing finish so that even complex surfaces can be effectively ground or polished.

BACKGROUND OF THE INVENTION 
This invention relates to a grinding or polishing device of the type 
consisting of one or more substantially circular grinding or polishing 
discs, each having a central hole and radial grinding or polishing 
segments arranged along the periphery thereof. 
Such rotating grinding or polishing devices are used, for example, for 
grinding or polishing furniture parts, such as louvered or panelled doors. 
However, it is very often difficult to obtain a good and uniform grinding 
or polishing finish, because the parts will often have a very complex 
shape with projections, hollows, grooves and the like. 
A rotating grinding or polishing device of this type is described in U.S. 
Pat. No. 2,879,631, disclosing a brush. This brush consists of a large 
number of slits or slotted sheets of stiff sheet material coated with 
abrasive materials, which sheets by the folding thereof, are retained in a 
metal channelform back element. 
This structure, however, is encumbered with several drawbacks. It is, for 
example, costly as well as inconvenient to use a metal channelform 
element. The manner of assembling the grinding or polishing disc is also 
disadvantageous because the segments cannot be fully joined together. This 
will have the effect of the segments relatively often breaking off. 
It is a further drawback that the segments can only with difficulty turn 
their abrasive surfaces in towards the object bacause they are made of a 
stiff material, such as thin spring steel. This will produce an uneven and 
poor grinding or polishing finish. 
Finally, this known structure is rather heavy, which will necessitate a 
comparatively powerful motor and which will also impair the polishing 
quality. 
All things considered, this known structure cannot grind or polish wooden 
objects, for example, which are not quite even, because the segments 
simply cannot follow the configuration of the object. At the same time, 
the brush is both expensive and difficult to manufacture. 
OBJECTS AND SUMMARY OF THE INVENTION 
The object of the invention is therefore to provide a lightweight and 
inexpensive grinding or polishing device that is capable of grinding or 
polishing even very complex surfaces. 
This object is achieved according to the invention in that each grinding or 
polishing disc is provided with two or more substantially parallel layers 
of grinding or polishing segments, and that the segment layers along the 
edge of the central hole are maintained together by a binding material 
situated between the layers. 
The grinding or polishing device according to the invention is very 
inexpensive to manufacture because no complicated metal parts are required 
for holding together the individual grinding or polishing discs. Thus, the 
grinding or polishing device is not heavy, which will make it possible to 
use a smaller and less expensive motor. Since the grinding or polishing 
segments are effectively retained, the grinding or polishing device can 
last for a comparatively long time. The grinding or polishing performance 
is good because the segments will bend in such a manner that the grinding 
or polishing coated surfaces will follow the surfaces of the object for a 
comparatively large part of a turn. 
The light segments can follow "hollows or grooves" in the object because 
the rotation will carry them outwards. The grinding or polishing quality 
will also be high because each individual segment can follow the object 
freely, but nevertheless have such stiffness that, for example, knots or 
projections are also ground or polished. 
As disclosed, a grinding or polishing disc according to the invention has 
along the entire circumference at the edge of the central hole thereof, 
binding material extending somewhat radially for forming a retaining area. 
There is thus achieved a high degree of durability of the grinding or 
polishing disc and, at the same time, a suitable stiffness of the 
retaining area. This stiffness has proved to be of great importance to the 
quality of the grinding or polishing finish because the segments must 
follow the configuration of the object but still engage the same with a 
certain pressure. 
If the two layers of segments, as disclosed, are formed integrally, the 
grinding or polishing disc being made from a substantially rectangular 
slitted sheet material as disclosed in copending U.S. Pat. No. 4,365,448, 
the entire disclosure of which is incorporated herein by reference, there 
is obtained a very easily manufactured and inexpensive grinding or 
polishing disc with the smallest possible consumption of material. 
Moreover, there is sufficient distance between two adjacent segments so 
that they are freely movable. 
It is advantageous if, as disclosed, the binding material is a 
heat-activatable material. It is thereby possible to easily form a 
suitably wide retaining area by pressing the grinding or polishing disc 
between two heated jaws. 
In a preferred embodiment of the invention, the heat-activatable material 
has the shape of a string. By at least letting the ends of the string 
meet, the string will keep the ring together, while at the same time, 
ensuring the stiffness in the retaining area. 
A further strong grinding or polishing disc is obtained if the string 
encircles the central hole several times, as is disclosed. It is thereby 
possible to quite exactly prepare the retaining area by means of the 
number of windings, and the ring is kept together in a safe manner. 
Finally, it is advantageous if the grinding or polishing device is designed 
as disclosed, the rings ensuring a sufficiently large distance between two 
grinding or polishing discs so that the segments thereof are freely 
movable.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings in detail, and initially to FIG. 1 thereof, there 
is shown a grinding or polishing disc 1 according to the present invention 
formed of two layers 2a and 2b formed of segments 2 radiating from a 
retaining area around a central hole 8. The grinding or polishing disc is, 
for example, made of cloth coated with an abrasive coating 9 but the use 
of other materials is also possible. 
As will particularly be seen from FIG. 2, the abrasive coating 9 is 
provided on the outside of the cloth layers. 
By the edge 3 which defines hole 8, the two layers have been joined by 
melting a string 4 of a heat-activatable material between the layers. 
There is thus obtained a retaining area being suitably stiff but 
nevertheless flexible. 
These properties are very important to an effective grinding or polishing 
finish. 
It is therefore possible to use materials other than heat-activatable ones. 
The use of various kinds of glue or the like is thus possible. 
During the grinding or polishing process, the segments 2 will bend so that 
the abrasive coating follows the surface of the object. If desired, the 
bending may be facilitated by weakening lines. 
FIG. 3 clearly shows how a number of grinding or polishing discs 1 are 
assembled to form a grinding or polishing device having intermediate rings 
7. 
Apart from retaining the discs 1, the rings 7 are intended to provide a 
suitable distance between the segments 2 so that these are freely movable. 
The rings 7 are advantageously made of foamed material such as 
polystyrene, the rings 7 thereby being light as well as strong. It is of 
course possible to make use of other suitable materials. One possible 
arrangement of the rings 7 and discs 1 is shown and described in copending 
U.S. Pat. No. 4,365,448, the entire disclosure of which has been 
incorporated herein by reference. 
The heat-activatable string 4 encircles the hole 8 several times thereby 
obtaing a strong disc with good properties. It has been found that 
grinding or polishing discs 1 having a diameter of approximately 30 cm, a 
central hole 8 of approximately 10 cm and a width of the segments of 
approximately 5 mm have outstanding abrasive properties. In this respect, 
it is important that the segments are of suitable width, since otherwise, 
it will not be possible to adjust the grinding or polishing process. 
Finally, the rings 7 are advantageously almost twice as thick as the width 
of the segments 2. 
It is essential to the grinding or polishing process that there is 
comparatively good space between the segments. The segments thereby do not 
become entangled during the process, which would result in reducing the 
abrasive effect and causing damage to the grinding or polishing device. 
It is also important that the segments are dimensioned so as to be able to 
freely follow the surface of the object. 
When working with lacquered objects, the present invention eliminates the 
need for an expensive, manual grinding or polishing process, because the 
small fiber formed by usual rough grinding methods can now for the first 
time be machined away by a grinding or polishing device according to the 
present invention. The present device possesses the optimum combination of 
distance between segments, flexibility of segments, stiffness in the 
retaining area and the possibility of fast rotation, namely between 900 
and 1200 revolutions per minute. Therefore, the grinding or polishing 
device according to the present invention has also proved to be superior 
to all other makes in the market since no grinding or polishing devices 
whatsoever can grind or polish with an equally high quality as the 
grinding or polishing device according to the present invention.