DE2349326A1 - SANDING GRAIN AND GRAIN BLEND - Google Patents

Description

Dr. Ludwig TSCHIPF and Dr. Franz HASTIK, both in Vienna (Austria)

Abrasive grain and abrasive grain mixture

Abrasive grains usually consist of corundum ₂ C ₃ ), silicon carbide (SiC), beryllium oxide (BeO), boron carbide (B ₄ C), borazon (BN) and diamond (C), whereby the crystals are ground to different grain sizes

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retain their characteristic fracture shape.

The fragmented and on a desired one Medium-diameter sized crystals or grains are bonded by a binder to form abrasive tools, Usually one uses as a binding agent depending on the processing case Kerairik, silicate, rubber, metal and synthetic resin. When manufacturing the grinding wheel, care is taken to ensure that a sufficiently large pore roughness is created the chips formed during the working process can migrate freely accordingly. By the great Pelative speed between the workpiece and the Abrasive bodies are created very much at the cutting point high temperatures, which lead to strong heating of the chips flying away f (their.

The advantage of grinding is that workpiece surfaces with a high degree of dimensional and shape accuracy and a shallow depth of pitch are economically produced can be. Hardened or otherwise heat-treated workpieces can go through grinding process can be machined without losing the heat treatment effect.

Disadvantages are the unfavorable machining conditions on a single grain, which lead to inadequate economic utilization of the abrasive grains. Because of the natural fracture shape of the small abrasive grains, the average rake angle is strongly negative. This makes chip formation very difficult and the high cutting forces required lead to high heating of the workpiece surface and the chips that migrate. The wear on the abrasive grains is therefore correspondingly high due to the high machining temperatures and forces. Furthermore, the wear of the abrasive grains that occurs during the machining process causes a continuously increasing wear surface on the free surface of the cutting body. This wear surface in turn causes strong frictional forces, the magnitude of which can reach and even exceed the actual cutting forces. About the growth

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To keep these forces within limits, the grinding wheel is cleaned with a dressing tool at certain time intervals newly trued and / or used a grinding wheel with a soft bond. At the Dressing, the abrasive grain is broken by the dressing tool, causing it to remove the disruptive wear surfaces loses. If a soft bond is used, a With a certain pressure, the abrasive grit broke out of the bandage, further inside the abrasive tool any abrasive grains with little or no wear surface on the surface of the abrasive and take part in the machining process. However, this process is associated with a high level of abrasion wear tied together.

Supported in particularly difficult processing cases today the grinding process is electrochemical. In this case, instead of an ordinary coolant uses an electrolyte.

To improve the grinding process, it has already been proposed to use thin-walled, hollow-spherical abrasive grains together with conventional abrasive grain, in Grinding wheels bound to use. The addition of the hollow spherical abrasive grain should also to the existing porosity in the binder further pore space can be created without through these the binder matrix is noticeably weakened will. A limit of 1-10% by weight of hollow spherical abrasive grain was set for grinding steel indicated, which means only a cooler grinding due to the more open structure that forms on the grinding wheel could be achieved. The higher the contact pressure, the fewer hollow balls should be used and the working speed, with which the effect of adding hollow spherical abrasive bodies was lost again, or was greatly reduced. The state of

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Technology therefore shows that the sole use of hollow spherical, thin-walled! Abrasive grain better known Execution does not lead to the expectation of favorable results. To remedy this deficiency is one of the aims of the present Invention that an abrasive grain in the form of a curved body or a fragment of a concerns such a body and is characterized in that the wall thickness s and diameter D are chosen so that a K value, which stands for s.D, is within the range sharpened in FIGS. 4 and 5, where as the wall thickness at any point, the one measured at this point normal to the crooked surface of the grain Distance between the grain walls and below the diameter that appearing under a microscope The largest dimension of the grain is understood and the diameter between O, O1 and 5 mm heat. According to the invention trained abrasive grains are particularly suitable for processing difficult-to-grind materials, such as e.g. hoarded or unhardened, high-alloy steel. The abrasive grain formed in accordance with the present invention gives when using it, it has a favorable rake angle, which means that there is only little thermal and mechanical stress at the cutting point occur, so that particularly heat-sensitive steels can be processed advantageously. try on a workpiece made of Ck 45 N resulted in a reduction in abrasive grain wear up to 45% of the previous wear. Furthermore, with the abrasive grain according to the invention there is a constant total wear area the grains per surface unit of the grinding wheel during the machining process achievable. This increases the corresponding force component while the grinding process continues not on, so that no significant changes in the grinding force occur. The ^ grinding forces both normal When using abrasive grains according to the invention, both for and in the machining direction are smaller than those that with the same machining performance with comparable ones Conventional grinding wheels can be measured. at

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Tests on workpieces made of hardened X 210 Cr 12 were able to reduce the grinding forces on grinding wheels, which were equipped with grain according to the invention, up to 25% of that of conventional grinding wheels to be used grinding forces can be achieved. Corresponding these low normal and circumferential forces can both the dimensional accuracy of the workpieces is increased as well as with the same drive power of the machine tool a higher cutting performance can be achieved. Furthermore, a dressing of the grinding wheel for the purpose of recovery the grip of the surface is omitted, so that the service life and the economic efficiency of the grinding tool is increased. There is an increase in the total wear area per unit area as a result of the cup-shaped Grain is not possible, the processing of hard types of material does not lead to "pressing" of the grinding tool, which up to now had to be compensated for by an appropriate choice of suitable bond hardness. It it should be pointed out that the stated effects not only when using with the inventive Abrasive grain-equipped grinding wheels, but also when the grain is in loose form, e.g. for lapping, is used.

Another object of the invention is an abrasive grain mixture which contains abrasive grains according to the invention, wherein in the manner according to the invention, the mixture contains at least two types of grain with different K values contains, the ratio of the K values of these types of grain lierrt between 1 and 100 and the proportion of curved bodies or fragments of such bodies in the abrasive grain mixture is at least 51% and the plague is formed by the usual full abrasive grain. Of the The advantage of the mixture according to the invention is that get all the advantages of the abrasive grain according to the invention remain, due to the mixture with grains of different shapes, however, a significantly higher mechanical strength of the abrasive grain mixture is achieved than it

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achieved with the grain according to the invention alone high machining performance on hard and difficult-to-grind materials, such as Hardened or unhardened high-alloy steels are possible.

The invention is explained in more detail below with reference to the drawing. Fs. Shows

Fig. 1 shows a Tfil of an abrasive article, the hollow form closed abrasive grains mixed with peel contains open abrasive grains,

Fig. 2 shows a toilet of an abrasive body, the hollow closed abrasive grains mixed with helical ones Contains abrasive grains,

3 also shows a part of an abrasive body, the shell-shaped open abrasive grains of various Types contains, and the

4 and 5 are diagrams from which the range for, for the dimension of the grain according to the invention essential K-value can be found.

In Fig. 1 is a section through a grinding wheel shown, which on the one hand made of hollow closed grinding grains 1 and on the other hand of shell-shaped open abrasive grains 2 consists, as is evident by a Splintering process can be obtained from closed hollow abrasive grains. The bond is denoted by 3.

In Fig. 2 is a section through an abrasive grain mixture shown, which on the one hand consists of hollow, closed abrasive grains 1 and on the other hand of screws for its own abrasive grains 4.

In Fig. 3 a section through an abrasive body with hollow open abrasive grains 2 is also mixed with hollow open abrasive grains 5 shown. the hollow open shape is achieved by a splintering process of hollow closed grains. The abrasive grains 5 have a different K value than abrasive grains 2. The bark is denoted by 3.

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Practical tests show that a clogging of the cuttings is not observed in the interior of the abrasive grain. The cause lies on the one hand in the extremely small size of the grinding chips, averaging 3 .mu.m with an average outer dimension and a length of 0.7 mm compared to the ground opening diameter of the hollow grains with an average of 100 .mu.m. As a result of the smooth inner surface of the abrasive grain and the constantly acting centrifugal forces during the grinding process caused by the rotation of the grinding wheel, the chips are thrown out of the opening immediately after leaving the machining zone.

From FIGS. 4 and 5, a diameter D of the abrasive grit each has an area for the K value to be taken, whereby then for the respective from this

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richly selected K value according to the relationship k = s.D the wall thickness of the grain can be determined or from the, the. ' K-value range assigned to the respective diameter the range of wall thickness can be determined. So it can be seen from Fig. 5 that a diameter of 1 mm, a range of the K value between 0.06 and 0.5 is assigned or due to s = K.D die Wall thickness can vary between 0. Of- and 0.5 mm.

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Claims (5)

Patent claims: Π J abrasive grain in the form of a curved wall Body or a fragment of such a body, characterized in that the wall thickness s and diameter D are chosen so that a K value that is suitable for s.D, lies within the hatched area in FIGS. 4 and 5, where as wall thickness any point, the distance between the grain walls and below the diameter the largest dimension of the grain that appears under a microscope is understood and the diameter is between 0.01 and 5 mm. 2. Abrasive grain mixture containing abrasive grains according to claim 1, characterized in that the mixture Contains at least two types of grain with different K values, the ratio of the K values of these types of grain between 1 and 100 and that the proportion of curved-walled bodies or fragments of such bodies in the abrasive grain mixture is at least 51% and the Pest is formed by the usual full abrasive grain. 3. Abrasive grain mixture according to .Anspruch 2, characterized in that that there are hollow closed abrasive grains and cup-shaped open abrasive grains (Fig. 1). 4. Abrasive grain mixture according to claim 2, characterized in that that it contains hollow closed abrasive grains and F-shaped abrasive grains (Fig. 2). 5. Abrasive grain mixture according to claim 2, characterized in that that it contains hollow open abrasive grains of various types (Fig. 3). 409815/10 57 -8th- Blank page