During molding of metal and wooden objects one of the most important moments is ensuring a properly smooth surface on the objects. Besides aesthetical aspects it is also necessary to protect the objects by providing them with a protecting layer and technology can be executed on a properly polished surface. Before painting or before applying any other protecting layer, for example a plastic protecting layer, or before a galvanization the most important phase is the proper surface preparing technology.

Ensuring smooth, homogenous surfaces is first of all possible with grinding papers fixed on various small machines. A well-known method of mechanical grinding is fixing grinding paper on a machine doing oscillatory motions. Another well-known solution is joining a grinding head a small machine, for example a machine drill and grinding is carried out by that.

In the state of the art patent application P 88 02446 published on 28 March 1990 makes known grinding wheel with an exchangeable grinding surface, which is suitable for surface technology of objects, materials, devices. The grinding wheel is composed of various materials, for example of wood, metal, plastic, textile and grinding material in a way, that a flexible material is joined the body of the wheel along the outline, on which a material provided with grinding material, preferably an exchangeable grinding band is fixed. The material provided with grinding material preferably a grinding band is fixed to the wheel with a flexible fixing element. The flexible fixing element is located in the cutting formed in the body of the wheel and has a flexible element joining the fixing element. Depending on the diameter of the wheel one or more flexible fixing element is provided.

Hungarian utility model HU U 2123 makes known a grinding device that can be fixed to small machines. The grinding device shown in this utility model has a fixing plate joining a rubber plate and grinding paper is fixed to the fixing plate. It is characterized by that the rubber plate has a threaded bushing and a threaded connection with lengthening shank is joined its threaded boring.

The general problem with the solutions made known so far is, that fixing of the grinding paper to the rubber plate is not satisfactory, because due to various lateral loading the threaded connector commonly used nowadays often breaks when the grinding paper is thrown away and so it is unsafe.

When working out the solution we set the aim to find a solution, which ensures, that no breaking occurs even in case of extremely dynamical use and which is much faster to fix than the conventional solutions.

When realizing the solution according to the invention we recognized, that if we apply a connector that can be made self-locking by twisting it with 90° for connecting the grinding head with the grinding wheel, then it is more suitable for bearing the shearing stress and it gets tightened during twisting in the fixing nest shaped deliberately for this purpose in the fixing part, then the set aim can be achieved.

The object of the invention is a connecting device for a grinding wheel to a grinding head, said device comprising of a grinding head provided with a fixing part and joined by a grinding wheel. The connecting device is characterized by that, a fixing nest serving as a fixing for a grinding wheel is formed in the bottom of the grinding head provided with a threaded connection on the upper part of the grinding head, said fixing nest is joined by a fixing plate, said fixing plate is preferably fixed by an adhesive through its support unit to the grinding wheel and said fixing plate is joined in a way, that-after a preferably 90° twisting-at the time of fixing a fixing flap placed on the upper part of the fixing plate closes in the fixing nest above a fixing shoulder in a self-locking way. The D1 diameter of an installing opening of the fixing nest is the same or bigger, than the Df diameter of the fixing flap of the fixing plate,

and the D 1 diameter of the fixing nest is gradually declining towards the closing direction and in closing position the D2 diameter of the fixing nest is smaller, than the Df diameter of the fixing flap, furthermore there are stops in the fixing nest to prevent further twisting and complete jamming.

In a preferred embodiment of the connecting device according to the invention, the inner diameter of the flexible rubber rim located in circle on the lower part of the grinding head is the same as the outer diameter of the support unit of the fixing plate.

In another preferred embodiment of the connecting device according to the invention, the threaded connection is joined by the driving axis of a small machine, or in given case said threaded connection is joined by a shank with a threaded flange. Both the threaded connection of the grinding head and the shank with lengthening threaded connection are preferably of the same key opening and of hexagon head. The raw material of the grinding head is preferably metal, in given case aluminum or steel, or plastic, or rigid rubber, the raw material of the fixing plate is preferably rigid plastic of high tensile strength and of high heat resistance, in given case ABS.

The solution according to the invention will be set forth with the accompanying drawings: Fig. 1 shows the lateral elevation of the solution according to the invention in half- elevation, half-section.

Fig. 2 shows the lateral elevation of the grinding wheel and the joining fixing plate.

Fig. 3 shows the top-view of the grinding wheel and the joining fixing plate.

Fig. 4 shows the inner formation of the fixing nest of the grinding head at the cross section A-A of the Fig. 1.

Fig. 1 shows the lateral elevation of the solution according to the invention in half- elevation, half-section. The solution comprises of the grinding head 4 provided with a fixing nest 5 and a grinding wheel 8 provided with a fixing plate 9 joining the fixing nest 5 of the grinding head 4. The grinding head 4 provided with connection 3 threaded on top can be seen on Fig. 1. The fixing nest 5 is formed in the bottom of the grinding head 4 providing fixing for the grinding wheel 8. The axis of the driving

small machine, or in given case a shank 1 ending in a threaded flange 2 is connected to the threaded connection 3 ensuring the drive of the grinding wheel.

The grinding head 4, the inner shape of the fixing nest 5, and the fixing shoulder 7 in the fixing nest 5 can be seen in half-section in Fig. 1. In case of the solution according to the invention the support 10 of the fixing plate 9 is connected to the grinding wheel 8. On the upper part of the fixing plate 9 there are two fixing flaps 12 below each there are grooves 11. During fixing the fixing flaps 12 of the fixing plate 9 should be inserted to the installing opening 13 of the self-locking fixing nest 5 formed properly in the bottom of the grinding head 4 and the fixing flaps 12 of the fixing plate 9 will be self-locked in the fixing nest 5 during the 90° twisting.

During the locking the fixing flap 12 will go behind the fixing shoulder 7 in the fixing nest 5, furthermore the support of the fixing plate 9 will rest against the bottom of the grinding head 4 as well. On the lower part of the grinding head 4 in circle there is a flexible rubber rim 6 providing flexible support and suitable oscillation absorption.

Fig. 2 shows the lateral elevation of the grinding wheel 8 and the joining fixing plate 9. The support 10 of the fixing plate 9 is connected to the grinding wheel 8 with adhesive. The lateral formation of the fixing plate 9, the fixing flap 12 on the upper part of the fixing plate 9 and the groove 11 below it as well as the centralizing cylindrical part 16 below the fixing flap 12 can be seen well in Fig. 2.

Fig. 3 shows the top-view of the grinding wheel 8 and the joining fixing plate 9. The fixing flaps 12 of Df diameter outer edge 15 shaped as two-direction extensions on the upper part of the fixing plate 9 can be seen in the figure.

Fig. 4 shows the inner formation of the fixing nest 5 of the grinding head 4 at the cross section A-A of the Fig. 1. The installing opening 13 is shown with dotted line in the figure the diameter D1 of said installing opening 13 is the same or bigger than the Df diameter of the fixing flap 12 of the fixing plate 9. This way the size of the installing opening 13 of the fixing nest 5 makes possible the easy connection of the

fixing plate 9 because its size is preferably the same as the Df diameter of the fixing flaps 12. The fixing nest 5 however is of D2 diameter in the closing direction, which is smaller, than the Df diameter, consequently the fixing flaps 12 will get tightened flexibly on their outer edge 15 in the fixing nest 5. Further twisting and undesired tightening are prevented by stops 14 in the fixing nest 5, because they close in the opposite direction, so it serves as suitable transmitter of rotating and grinding energy.

The tightening prevents the grinding head 4 from twisting back from the axis of the machine. The middle, centralizing cylindrical part 16 of the fixing plate 9 serves the absorption of the lateral shearing forces while the fixing flap 12 in the fixing nest 5 serves the self-locking and prevents further twisting.

In case of a preferred embodiment of the solution according to the invention the support 10 of the fixing plate 9 fits into the inner diameter of the rubber rim 6 of the grinding head 4, this way ensuring an even safer direction for the grinding wheel 8, and makes possible an accurate circumduction, which is further increased by the inner fixing shoulder 7. In a preferred embodiment the threaded connecting part 3 of the grinding head 4 as a lengthening shank 1 with thread is of key opening and of hexagon head.

The grinding head 4 actually has a connecting part 3 with thread, which joins a lengthening shank 1 of required length, or joins directly the axis of the driving machine. Here the use of the same threads is preferable, because in that case the grinding head 4 can be used either by inserting or without inserting the shank. The joining threads are of the same diameter, consistent with the axis of the driving machine.

The Df diameter of the fixing plate 9 and the D1 diameter of the installing direction of the fixing nest 5 are the same, preferably 30 mm. In the closing direction the D2 diameter of the fixing nest 5 is preferably 28-29 mm and the definite dimension is chosen in accordance with the joining depending on the material of the fixing flap 12 in such a way, that the fixing flap 12 in the fixing nest 5 should close deforming

flexibly, tighten, and it should be taken out without damage. Dimensions should be determined according to a tight tolerance fitting.

The inner diameter of the flexible rubber rim 6 located on the lower part of the grinding head 4 in circle providing flexible support and suitable oscillation absorption is preferably the same as the outer diameter of the support 10 of the fixing plate 9 which also promotes centralization and transmitting of lateral forces. This way the support 10 of the fixing plate 9 fits into the inside of the flexible rubber rim 6, so the fixing plate 9 is concentrically fixed and every level of the fixing plate 9 is supported.

The material of the fixing plate 9 should be durable, in given case for example aluminum, steel, or plastic, or rigid rubber. The material of the fixing plate 9 is inexpensive, easy and fast to produce, of proper tensile strength, heat-resisting rigid plastic, preferably ABS. In given case the connecting of the grinding wheel 8 and the fixing plate 9 takes place with adhesive in a way, where the support 10 of the fixing plate 9 is joined with the back of the grinding wheel 8. Connecting of the fixing plate 9 and the grinding wheel 8 can be realized by injection molding following the proper surface technology process. Producing of the grinding wheel 8 takes place from sand- paper, from which the wheels are cut, and the fixing plate 9 will be glued on the back by heat-resistant adhesives of great mechanical load-bearing capacity. The paper serving as raw material for the grinding wheel 8 should bear a speed of 20 m/sec.

The advantage of the solution according to the invention is, that the grinding wheel can be easily and quickly exchanged in the grinding head. It replaces the fixing by a threaded boring applied previously. In the solution according to the invention in the grinding plate there is an appropriately shaped self-locking fixing nest, into the opening of which the fixing flaps of the fixing plate can be fitted. By the 90° twisting of them self-locking can be ensured. During use the grinding wheel can not break and installing is much faster. The middle centralizing cylindrical part of the fixing plate ensures absorption of the lateral shearing forces occurring during grinding, so the shearing surface is many-fold more of the conventional solution with screws. Due to this its use is significantly more advantageous from point of view of safety.