EP0865879A2 - Abrasive grinding disc and method of manufacturing the same - Google Patents

Abstract

The grinding disc comprises an outer crown (4), and intermediate conical zone (6), and a central disc-shaped section (8). The peripheral zone of the crown is equipped with a series of abrasive segments (20) with ventilation holes (12) between. The abrasive segments are basically in the shape of circumflex accents, each with one wing (22) which extends along the edge of the disc while the other points towards the centre. The abrasive segments have parabolic spiral surfaces and act as vanes for ventilating the disc.

Description

The present invention relates to an abrasive disc for grinding of materials, comprising a support provided with segments comprising an abrasive material and a binder coating.

Grinding tools exist in a large variety of shapes and sizes, suitable for a wide range of applications.

Historically, they were developed on the basis of abrasive particles (alumina oxide, carbide silicon ...) incorporated in organic binders or vitrified.

The wear of this type of tool being very important, we developed grinding wheels made up of grain segments of diamond set in a coating binder associated with a support metallic by welding, soldering or mechanical attachment or still grinding wheels obtained by direct sintering of the binder coating crimping the diamond grains on the body tool metal. Many uses of these tools have place under abundant watering which has the merit of cooling the tool and to remove the ground material.

In the case of dry grinding, the dust released by the operation must be evacuated as soon as they are formed. We thus prevents clogging of the active surface of the disc, and reduced efficiency and overheating resulting detrimental.

Suction or blowing devices are intended for this purpose but do not always perform their function.

Diamond grinding abrasive discs have been developed for portable machines powered by a operator. These tools generally have the form of a disc and consist of a support having an area crown-shaped device, a median shaped area conical, and a disc-shaped interior area. Of abrasive segments, shaped like a crown sector, are fixed on the periphery of the peripheral zone. These segments can be arranged in a single row in the form of circle, or on two or more concentric rows. Of openings in the support allow to force air circulation to cool the segments abrasives during work, and take away the chips and grinding dust.

Discs with a single row of segments lead to jerky grinding work, and a state of the ground surface with streaks. Good support from the grinding tool on the work surface is difficult to achieve.

Discs with two or more rows of segments allow better support of the grinding tool, and lead to more regular grinding work. These tools, however, have the disadvantage that due to baffles imposed on the air circulation, the cooling and removal of shavings and dust from grinding are difficult to perform.

The invention aims to remedy in a simple way and effective at the disadvantages mentioned above.

The subject of the invention is an abrasive grinding disc consisting of a support comprising a peripheral zone in crown shape, a conical middle area and a central disc-shaped area. The peripheral zone is provided with abrasive segments. Openings allowing air intake or air supply is provided in this peripheral zone. The abrasive segments essentially have a "L" shape or circumflex accent, and have a wing extending substantially along the periphery of the disc, and a wing extending substantially from the periphery towards the center of the disc. The so-called "L" shaped segments or circumflex accent can present a wide range of shapes, curvatures and widths, without departing from the scope of the invention. Preferably, the abrasive segments have the shape of a dawn, and the profile of this dawn is determined so that when the disc is spinning, the air sucked or blown flows with an absolute speed according to the spokes of the disc, thus facilitating the circulation of this air. To this end, the abrasive segments have advantageously a profile in the form of a parabolic spiral. The abrasive segments can include diamond grains and a coating binder.

• la Fig. 1 est une vue de face d'un disque de meulage suivant l'art antérieur;
• la Fig. 2 est une vue latérale d'une machine de meulage portable;
• la Fig. 3 montre l'état de surface obtenu après meulage au moyen du disque de meulage représenté à la Fig.1;
• les Figs. 4, 5 et 6 sont semblables aux Figs. 1,2 et 3, mais relatives à une autre forme de disque de meulage suivant l'art antérieur;
• la Fig. 7 représente, pour moitié, un disque de meulage suivant l'invention, vu de face;
• la Fig. 8 est une vue en perspective cavalière, et en éclaté, d'une partie d'un disque de meulage suivant l'invention;
• la Fig. 9 illustre schématiquement le mode de détermination de la forme optimale d'un segment abrasif.

Other characteristics and advantages of the invention will appear on reading the description which follows, reference being made to the appended figures. In these figures:

• Fig. 1 is a front view of a grinding disc according to the prior art;
• Fig. 2 is a side view of a portable grinding machine;
• Fig. 3 shows the surface condition obtained after grinding by means of the grinding disc shown in Fig.1;
• Figs. 4, 5 and 6 are similar to Figs. 1,2 and 3, but relating to another form of grinding disc according to the prior art;
• Fig. 7 shows, for half, a grinding disc according to the invention, seen from the front;
• Fig. 8 is a perspective view, in exploded view, of a part of a grinding disc according to the invention;
• Fig. 9 schematically illustrates the method of determining the optimal shape of an abrasive segment.

Figure 1 shows a grinding disc 2 according to the prior art, consisting of a support comprising a peripheral zone in the shape of a crown 4, a zone conical median 6, and an interior shaped area 8. These three areas are centered around the same axis. Abrasive segments 10, in the form of a sector of crown, are arranged on the face of the peripheral zone in the shape of a crown 4, at its periphery. Openings of air passage 12 are formed through the support. These 12 openings can be made in the middle area of conical shape 6. Forced air circulation is established at through these openings 12, and makes it possible to cool the abrasive segments 10 and take away the chips and dust from grinding.

If when using such a grinding disc 2 by means of a portable grinding machine 14, the operator apply said machine flat on the surface to be ground, bringing the entire peripheral zone 4 into contact simultaneously with the surface to be ground, then it is difficult to maintain the machine correctly in position. The operator has therefore naturally tend to tilt his machine as well as shown in Fig. 2. by angle A, so as not to carry on the surface to be ground only a single portion of the area peripheral 4. This results in grooves 16, which harm the quality of the surface obtained.

In the variant of a grinding disc according to art anterior 2, shown in Figs. 4, 5 and 6, we have arranged the abrasive segments 10 on two concentric circles. The operator can support his machine more horizontal, and the risk of creating the grooves 16 is reduced. However, in this variant, the air used to cool the abrasive segments 10 and for removing the chips and the dust must travel a path with many baffles, shown in FIG. 4 by arrows B. We must then either use ventilation power important, or be satisfied with a cooling of the segments 10 and a dust and chip evacuation mediocre.

Fig. 7 shows a grinding disc 18 according to the invention, seen from the front. Identical elements are numbered in the same way as in Figs. 1 and 4. The abrasive segments 20 have an "L" or accent shape circumflex, and have a wing 22 extending substantially along the periphery of the disc 18, and a wing 24 extending substantially from the periphery towards the center of the disc, degressively. This provision makes it possible to obtain that any circle in the peripheral zone has material abrasive, while having a more active surface area important around the edge of the disc 18.

In an improved variant of the invention, one gives to the segments 20 a shape of a turbine blade such that, when the disc 18 rotates in the direction indicated by the arrow T, the cooling air drawn in through the openings 12 flows from the outside to the inside of the disc 18 in a substantially radial path. These segments 20 therefore present a minimal obstacle to the circulation of the air. Other combinations of air flow direction, the direction of rotation of the grinding disc 18 and the shape blades provide the same result. The same effect can be achieved, for example, with the shape of segments 20 of FIG. 9, the air being blown in by the openings 12, i.e. circulating from the center of the disc 18 towards its periphery, and the disc 18 rotating in the direction of the arrow T.

The shape of the segments 20 according to the invention, shown in Fig. 7, therefore has the advantage of facilitate air circulation. It also presents the advantageous characteristic that the active surface, i.e. the contact surface between the segments 20 and the grinding surface grows from inside the disc 18 towards its periphery. This results in more grinding work regular.

Fig. 8 is a perspective view of a disc grinding 18 according to the invention. It highlights the shape of the support comprising a peripheral zone 4 and a inner zone 8, located in offset parallel planes, and connected by a conical median zone 6, and taking thus the shape of a flattened bell.

Fig. 9 schematically illustrates the method of determining the shape to be given to an abrasive segment 20 in order to optimize the circulation of the air blown through the openings 12. The air travels through the peripheral zone from a circular zone delimited by R _a and an exit zone bounded by R _c . For a particle of circulating air, we have the following vector relation between the absolute speed, V _a , the relative speed V _r , and the speed of drive V _e : V at = V r + V e (Absolute speed = relative speed + drive speed).

The drive speed V _e is imposed by the rotation of the disc 18. If we want the absolute speed V _{a to} be directed radially, we can build the relative speed V _r . The curvature of the abrasive segment 20 is then directed along V _r . It is thus possible to construct the optimal shape of an abrasive segment 20 respecting aerodynamic constraints.

The speed of training is given by V e = ω * r where ω is the angular speed of rotation, and r the radius.

The air flow Q passing through a section S between two segment 20 being constant from the entry radius R _a to the exit radius R _c , we have Q = V at * S

The air passage section S increases from the center to the periphery according to the equation: S = 2 * π * r * h where h is the thickness of a segment.

In the triangle ABC, we have Tanα = V e V at = ω * r Q 2π * r * h is Tanα = k * r 2 where k is a constant depending on the air flow Q, the angular velocity ω, and the height h of a segment 20.

The expression of the optimal curve, in polar coordinates r,  can be obtained by considering the point A of coordinates r,  and the infinitely neighboring point on the curve, C, of coordinates r + dr,  + d. In the same triangle ABC, we have the relation Tan α = r * d  dr

By comparing equations (1) and (2), we obtain from dr = k * r is  = K * r 2 2 + Coast

The optimal theoretical shape of segment 20 is therefore that of a parabolic spiral. A very significant improvement in air circulation can be obtained by means of segments 20 whose shape approximates that guided by the above theory, without having to be identical to the theoretical shape. In addition, thanks to the segments 20 according to the invention, the active grinding surface is distributed evenly between the inner radius R _a and the outer radius R _b , and is maximum at the periphery, where it is required. The abrasive segments according to the invention allow a substantial improvement in the quality of the ground surface obtained, in the ease of handling of the tool by the operator, and in the longevity of the tool, thanks to better ventilation and better elimination of grinding chips and dust.

Claims (4)

Abrasive grinding disc (18) consisting of support comprising a peripheral zone in the shape of a crown (4), a conical middle zone (6) and a zone central disc-shaped (8), peripheral area (4) being provided with abrasive segments (20), openings allowing suction or blowing of air being provided in the peripheral zone (4), characterized in that the abrasive segments (20) are substantially in the form of an accent circumflex, and have a wing (22) extending substantially along the periphery of the disc (18), and a wing (24) extending substantially from the periphery towards the center of the disc (18). Abrasive grinding disc (18) according to the claim 1, characterized in that the abrasive segments (20) have essentially the shape of a blade, the profile of this dawn being determined so that when the disc (18) is rotating, the air sucked or blown flows with an absolute speed along the spokes of the disc. Abrasive grinding disc (18) according to the claim 2 characterized in that the abrasive segments (20) have a parabolic spiral profile. Abrasive segment (20) suitable for use in a abrasive grinding disc (18) according to any one of previous claims.

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