EP0229983A2 - Sound-deadened grinding wheel - Google Patents

Abstract

Multi-layer grinding wheels are built up in layers for sound insulation with the interposition of at least one layer of vibration-damping materials, the layer of vibration-damping materials being introduced into the mold in the form of a fine-grained, free-flowing powder and / or granulate. The powder or granulate can consist of elastomers that can withstand heat of more than 110 ° C. The elastomer can be mixed with synthetic resin. The addition of filler promotes the processability of the mixture and improves the granulation ability.

Description

The invention relates to a process for the production of multi-layer grinding wheels, in particular multi-layer cutting and grinding wheels for free-hand grinding, in which mixtures of abrasive grain and binder, and optionally fillers and possibly reinforcements, are introduced in layers in a mold with the interposition of at least one layer of vibration-damping materials be pressed into a blank and the blank obtained is cured.

During grinding and cutting, but especially during free-hand grinding, vibrations occur which lead to considerable noise pollution, which vibrations occur both on the workpiece and on the drive machine and on the grinding wheel itself. If it is still possible with stationary machines to at least partially dampen these vibrations, or to encapsulate the machine as such and thus reduce noise for the operating personnel, this option is available when working with hand grinders in which cutting or grinding discs, in the generally referred to as flex disks, generally not used. In the course of increasing environmental awareness, there is therefore a considerable need for grinding wheels which have a reduced noise level when used. Grinding wheels, which tend to generate less vibrations due to their structure, are called sound-absorbing grinding wheels and are known as such from DE-OS 26 10 580, DE-OS 26 32 652 and AT-AS 46 15/82. All these proposals have in common that damping layers are arranged between the actual grinding layers, which are made of a polymer or a vibration-damping film, for. B. of nitrile rubber.

However, the processes for producing these known grinding wheels are very complex. For example, DE-OS 26 32 652 describes connecting at least two finished, so-called "grinding plates" with a certain diameter-thickness ratio to one another by means of a polymer layer which is at least 0.2 mm thick and at most the thickness of the "grinding plates" having. The polymer, which can be an adhesive, is placed in the form of a solution, a paste or in a liquid or molten state between the two "grinding plates" and then dried, hardened or solidified in order to firmly bond the two "grinding plates" together . A can be used as the polymer thermoplastic resin are used, however, curable plastics are preferably used by heat treatment.

The process is very complex since, in this process, finished “grinding plates” first have to be produced, which are subsequently connected to one another.

DE-OS 26 10 580 also assumes that several thin grinding wheels forming the layers of abrasive material are coated with a binder, placed on top of one another and pressed. To achieve greater thicknesses of the damping layers, disks made of thermoplastic film and disks made of abrasive material can also be alternately stacked and pressed together at temperature, so that the thermoplastic material bonds with the disks made of abrasive material.

Deviating from the two above-mentioned documents, which are based on an already finished "sanding plate", AT-AS 46 15/82 provides that a vibration-damping film, for. B. of nitrile rubber, is placed and pressed with the abrasive grain. The abrasive blank produced in this way is clamped between packing plates and cured in the oven. The fact that in each case a sheet of nitrile rubber punched for the shape or this sheet is first laminated onto the fabric and then has to be placed in the press together with it and after the pressing the grinding body blanks clamped between packing plates have to be cured in the oven, the process is extremely time-consuming and therefore labor-intensive.

Another disadvantage is that the pressed blank always springs slightly after pressing, which is due to the elasticity of the inserted vibration-damping film. This worsens the connection with the adjacent abrasive grain layers, so that there is a risk that individual areas of the abrasive grain layers do not touch the inserted film layer and there is no bond here.

The object of the present invention is therefore to demonstrate a method which ensures perfect adhesion between the abrasive and the sound-absorbing material over the entire surface of the layer and in which this sound-absorbing layer can also be applied and applied quickly and easily.

This object is achieved by a method for producing multi-layer grinding wheels, in particular cutting and grinding wheels for free-hand grinding, in which mixtures of abrasive grain, binder and, if appropriate, fillers and, if necessary, reinforcements are layered under Interposition of at least one layer of vibration-damping materials is introduced into a mold, pressed into a blank and the raw material obtained is cured, with the characteristic feature that the layer or layers of vibration-damping material in the form of a fine-grained, free-flowing powder or granulate in the Form are introduced.

Due to the fact that the vibration-damping material is used in powder and / or granulate form and is also fine-grained, the applied layer automatically adapts to the preceding and following layer in its surface structure, i. H. there is no free space between the individual layers after they have been pressed together. The powder or granulate also ensures that there is no undesirable springing after pressing the grinding wheel, since abrasive grain areas protruding from the abrasive grain layer or the reinforcement are embedded in the layer of vibration-damping material from the outset and therefore cannot press against a compact surface, which leads to Springing leads.

Since the blank does not spring open, there is also no need for intermediate storage and curing in the oven under tension. The advantage over the known prior art is therefore not only in the faster possible introduction of the powdered or granular material on commercially available presses, as has been used for a long time for production the grinding wheels are used, but also in that no additional work is required after the pressing process.

An advantageous embodiment of the invention provides that at least one elastomer is introduced as a powder or granulate, which withstands a heat load of more than 110 ° C.

In addition to various types of natural and synthetic rubber, butyl rubber, nitrile rubber, for example in the form of Perbunan N, neoprene, fluoroelastomers, polyacrylates, polyurethanes, silicone rubber, polysulfite rubber and hypalon, are also suitable here. All of these elastomers have to be more or less modified to withstand the required heat load and still have the elasticity required to reduce the sound level.

Eine weitere vorteilhafte Möglichkeit ist, als Pulver oder Granulat eine Mischung aus einem oder mehreren Kunstharzen und einem oder mehreren Elastomeren einzubringen. Die Verwendung eines Kunstharzes in Verbindung mit dem Kautschuk ergibt eine bessere Verbindung zwischen schalldämpfender Schicht und dem Schleifkorn, das als solches ja ebenfalls kunstharzgebunden ist. Die Wahl des Kunstharzes richtet sich dabei zum ersten nach der Temperaturbeständigkeit, zum zweiten aber nach der Verträglichkeit mit dem Kautschuk und dem Kunstharz, das als Bindemittel für das Schleifkorn beim Aufbau der Schleifscheibe eingesetzt wird. Bei Verwendung der üblicherweise für kunstharzgebundene Schleifkörper eingesetzten Phenol-Formaldehydharze kann als Kunstharz für die Dämpfungsschicht ebenfalls ein Phenol-Formaldehydharz eingesetzt werden. Auch ist der Einsatz weiterer Duroplaste, wie z. B. Melaminharz, Harnstoffharze und Polyesterharze denkbar.The examination of various damping layer materials showed that the compression of cylindrical model bodies under defined conditions, ie load 5 kp, dimension: diameter 15 mm, height = 20 mm, gives a very good statement about the reduction of the sound level during the later grinding process. Sound absorption increases with increasing elasticity. At the same time, however, the processability of the damping layer mixture and the strength of the soundproofed grinding wheel deteriorate. Again Table 1 shows that the best results in terms of sound level are achieved with a compression between 4.2 and 18.4%. With an upsetting above 24%, the damping layer mixture was difficult to process, and the drop in strength in the finished, sound-damped grinding wheel was so great that it could no longer be used.

Another advantageous possibility is to introduce a mixture of one or more synthetic resins and one or more elastomers as powder or granulate. The use of a synthetic resin in connection with the rubber results in a better connection between the sound-absorbing layer and the abrasive grain, which as such is also bonded with synthetic resin. The choice of synthetic resin is based on the first Temperature resistance, but secondly it is compatible with the rubber and synthetic resin that is used as a binding agent for the abrasive grain when building up the grinding wheel. When using the phenol-formaldehyde resins commonly used for synthetic resin-bonded abrasives, a phenol-formaldehyde resin can also be used as the synthetic resin for the damping layer. The use of other thermosets, such as. B. melamine resin, urea resins and polyester resins are conceivable.

Epoxy resin is particularly suitable because of its high strength and the good connection to the phenolic resins and the rubber.

A preferred embodiment of the invention provides that an epoxy resin is mixed with a nitrile rubber in a ratio of 10:90 to 70:30.

As the epoxy resin content increases, the sound absorption decreases and the strength of the soundproofed grinding wheel increases. The optimal range for sound absorption and grinding performance is when 15 to 25% epoxy resin is added to the nitrile rubber.

The handling of the sound-absorbing material is a particular difficulty in the manufacture of the sound-absorbing grinding wheels. More or less all of them can be used well Materials have a high stickiness and are therefore not free-flowing. Stickiness is to be understood as meaning that the individual particles accumulate to form larger agglomerates, ie the material is of inhomogeneous consistency, and agglomerations form, which leads to an uneven distribution when pressed. This also makes the finished grinding wheel inhomogeneous. In addition, the material adheres to the slides of the press.

Of particular importance is therefore the embodiment of the invention, which provides that the mixture is homogenized with the addition of a filler.

The homogeneous mixture obtained in this way is tack-free and therefore easy to incorporate into the mold. However, there is a risk that especially mixtures of fine powder will dust. An advantageous embodiment of the invention therefore provides that the mixture is brought to a granulate size of 50 to 2,000 μm in a granulator with the addition of filler.

The granulation is simplified by the addition of the filler, at the same time the stickiness is reduced so much that a free-flowing granulate results. On the one hand, the granulate size is important for the flowability, on the other hand it represents a requirement that depends on the grain size of the abrasive grains required for the grinding wheel is dependent. So you will always try to use a finer granulate than the abrasive grain used for the grinding wheel in order to achieve the densest possible packing and thus a good connection between the abrasive grain and the damping layer.

According to a preferred embodiment of the invention, up to 5% inorganic filler such as MgO, ZnO, talc or marble powder is added to the mixture. All of these fillers reduce the stickiness considerably, without this hindering the reactions when the grinding wheel hardens.

Another advantageous embodiment of the invention provides that a mixture of cork powder and synthetic resin is introduced as powder or granulate. The cork flour expediently has a grain size that is between 50 and 1,000 μm, epoxy resin is expediently used as the synthetic resin.

The invention is explained below using examples.

example 1

Undamped grinding wheel from standard series production.
Grinding wheel diameter 178 mm
Thickness 8 mm
22 mm hole.
Electro corundum is used as the abrasive grain. The Grain designation corresponds to the Fepa standard. A mixed grain consisting of 25.9% by weight of grain 24;
25.9% by weight grit 30 and
25.9% by weight grit 36.
It was added as a binder
3% by weight of phenol-formaldehyde resol, commercially available under the name Bakelite Resol 433,
11.3% by weight phenol-formaldehyde novolak, commercially available under Bakelite Novolak 227,
4% by weight pyrite,
4% by weight cryolite.

300 g of the resol 433 were added to 7,780 g of the corundum mixture and mixed in a planetary stirrer for five minutes. The wetted grain was then mixed with 400 g pyrite and 400 g cryolite and 1120 g novolak 227. Resulting agglomerates and agglomerations were screened off. 300 g of the homogeneous, free-flowing grinding wheel mixture obtained in this way were evenly distributed in a press mold, and in addition two external and one internal fabric reinforcement were introduced. The mixture was pressed into disks with an outside diameter of 178 mm, a bore diameter of 22 mm and a disk thickness of 88 mm. The blank obtained was placed on a stack with several other blanks of the same type and cured according to a temperature curve customary for phenolic resins, ie heating up to 90 ° C. in four Hours; Heating up to 120 ° C in three hours, holding time at 120 ° C five hours, heating up to 180 degrees in three hours, holding time at 180 ° C two hours, then cooling to room temperature.

Example 2

With the same structure, i.e. H. Arrangement of the fabric reinforcement in the outer areas and in the inner area and the same production process, an electrical corundum of grain 30 was used as the abrasive grain, which is ceramic coated, i. H. that the surface of the grain is partially coated with silicates to improve the adhesion with the binder.

75.8% by weight of aluminum oxide grain size 30
3% by weight phenol-formaldehyde resol, commercially available under the name Bakelite Resol 433
13.5% by weight phenol-formaldehyde novolak, commercially available under the name Bakelite Novolak 227
5% by weight cryolite
0.7% by weight of lime.

Example 3

Silenced grinding wheel according to the invention.

The formulation of the grinding wheel mixture and its production correspond to example 1. The grinding wheel consists of three grinding layers, two damping layers and three fabric reinforcements. 270 g of grinding wheel mixture were divided into three layers, so that 90 g were used per layer. 40 g of damping material were introduced as the damping layer, which were divided into two layers of 20 g each. The layers were alternately filled into the mold, with the grinding wheel mixture as the lowest, and a fabric reinforcement was inserted over the damping layers. The blank pressed to nominal size was cured as in Example 1, the thickness of the damping layer after curing averaged 1.3 mm. To produce the damping layer, 79% by weight of a nitrile rubber, which is commercially available under the name Hycar, was mixed with 20% by weight of an epoxy resin, commercially available under the name Araldit, and 1% by weight of magnesium oxide (MgO). For this purpose, 790 g hycar resin, 200 g araldite and 10 g MgO were stirred for five minutes in a planetary stirrer, the addition of MgO improving the processability of the mixture, ie avoiding caking and lump formation. The powder obtained had an average diameter of 100 μm.

Example 4

Structure The formulation and manufacture of the noise-dampened grinding wheel corresponds to Example 3 with the exception of the damping layer. The damping layer consisted of 41.7% by weight of cork powder with an average diameter of 250 µm, 16.6% by weight of a wetting agent, commercially available under SZ 449 (Bakelite) and 41.7% by weight epoxy resin, commercially available under SB 330 (Bakelite). 417 g of cork flour were mixed with 166 g of humidifier SZ 449 for five minutes. The moistened cork flour was then mixed with 417 g of epoxy resin powder SP 330 and stirred for a further five minutes.

Example 5

The formulation of the grinding layer corresponds to example 2. The formulation of the damping layer corresponds to example 3. Two damping layers were introduced.

Example 6

The formulation of the abrasive layer and the position of the fabric reinforcement correspond to Example 2, but an additional damping layer, the thickness of which was 2.5 mm, was introduced before the middle fabric reinforcement was inserted.

Example 7

The formulation of the grinding wheel mixture corresponds to Example 2, the formulation of the damping layer to Example 3. In contrast to Example 3, however, the damping layers were arranged on the outer layers directly behind the fabric reinforcements, so that they included the grinding wheel mixture.

Example 8

Corresponds to example 6, but a mixture of 10 was used as the damping layer material % By weight of epoxy resin and 90% by weight of nitrile rubber.

Example 9

Corresponds to Example 6, but a mixture of 30% by weight epoxy resin and 70% by weight nitrile rubber was used as the damping layer material.

The disks manufactured according to the aforementioned nine examples were subjected to a grinding test together with a commercially available disk in accordance with AT-AS 46 15/82 (example 10 in Table 2). It was ground with an angle grinder from Bosch, type 060 1331, the sound level was measured in front of a closed grinding cabin at a distance of 2 m from the workpiece. The intrinsic noise of the angle grinder was 67 dBA. A device from Rhode and Schwarz ELDO 4, measuring range 16 Hz to 16 KHz using an A filter was used as the measuring device. A tube made of St 35 with a diameter of 191 mm and a wall thickness of 17 mm was ground. The grinding time was 10 minutes.

und die Zerspanung

Es ergaben sich dabei folgende Werte.

In addition to the sound level (dBA), the Q factor was determined

and machining

The following values resulted.

• Figur 1 zeigt die Seitenansicht einer gekröpften Schrupp-Flexscheibe im Schnitt,
• Figur 2 in starker Vergrößerung einen Ausschnitt von Figur 1,
• Figur 3 die Seitenansicht einer geraden Schrupp-Flexscheibe im Schnitt mit zwei Dämpfungseinlagen,
• Figur 4 in starker Vergrößerung einen Ausschnitt aus Figur 3
• Figur 5 zeigt die Seitenansicht einer gekröpften Schrupp-Flexscheibe im Schnitt mit einer Dämpfungsschicht aus Kork,
• Figur 6 in starker Vergrößerung einen Ausschnitt aus Figur 5.

The invention is described below with reference to the drawings.

• FIG. 1 shows a sectional side view of a cranked roughing flexible disk,
• FIG. 2 shows a section of FIG. 1 in high magnification,
• Figure 3 shows the side view of a straight roughing flexible disk in section two cushioning inserts,
• FIG. 4 shows a section of FIG. 3 in high magnification
• FIG. 5 shows the side view of a cranked roughing flexible disk in section with a damping layer made of cork,
• FIG. 6 shows a section of FIG. 5 in high magnification.

As can be seen from FIGS. 1 and 2, a grinding wheel 1 consists of several layers which are successively inserted into the hollow shape of the press during the production process. First, a fabric reinforcement 5 is applied to the annular flange 3 according to the two figures mentioned, to which the abrasive layer made of abrasive grain 6, which is coated with binder 7, is then applied by means of a slide. Over this layer, the vibration-damping material is applied in the form of a powder, which forms the damping layer 8 after the fully pressed pane has hardened. A further fabric reinforcement 5 is placed on the powder made of vibration-damping material, then a second layer of abrasive grain 6 coated with binder 7 is applied, and a third fabric reinforcement 5 is placed over it as a finish. The layer structure achieved in this way is pressed to the desired dimension and then cured as described.

FIGS. 3 and 4 show the structure of a grinding wheel with two damping layers 8 and three fabric reinforcements 5, the fabric reinforcement 5 being arranged both outside and in the middle of the flexible disk 1scheibe.

FIGS. 5 and 6 differ from FIGS. 1 and 2 in that the damping layer 8 continues to consist of individual particles, namely of cork particles 4 coated with synthetic resin 4ʹ, even after pressing and curing. The other structure of this disc 1ʺ is identical to that according to Figure 1 or 2.

Claims (8)

1.Procedure for the production of multi-layer grinding wheels, in particular multi-layer cutting and grinding wheels for free-hand grinding, in the form of a blank in the form of layers in the form of mixtures of abrasive grain, binder and, if applicable, fillers and, if necessary, reinforcements, with the interposition of at least one layer of vibration-damping materials are pressed and the blank obtained is cured, characterized in that the layer or layers of vibration-damping material are introduced into the mold in the form of a fine-grained, free-flowing powder and / or granulate. 2. The method according to claim 1, characterized in that at least one elastomer is introduced as a powder or granules, which withstands a heat load of more than 110 ° C. 3. The method according to claim 1, characterized in that a mixture of cork powder and synthetic resin is introduced as powder or granules. 4. The method according to claim 1, characterized in that a mixture of one or more synthetic resins and one or more elastomers is introduced as powder or granules. 5. The method according to claim 4, characterized in that an epoxy resin is mixed with a nitrile rubber in a ratio of 10:90 to 70:30. 6. The method according to any one of claims 4 and 5, characterized in that the mixture is homogenized with the addition of filler. 7. The method according to any one of claims 4 and 5, characterized in that the mixture is brought to a granulate size of 50 to 2,000 microns in a granulator with the addition of filler. 8. The method according to any one of claims 4 to 7, characterized in that the mixture up to 5% inorganic fillers, such as. As MgO, ZnO, talc or marble powder can be added.

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