WO2015040172A1

WO2015040172A1 - Abrasive medium comprising a phosphate-based filler

Info

Publication number: WO2015040172A1
Application number: PCT/EP2014/070023
Authority: WO
Inventors: Gunnar BÜHLER; Herbert PÜTZ; Thorsten KONZACK
Original assignee: Rhodius Schleifwerkzeuge Gmbh & Co. Kg
Priority date: 2013-09-20
Filing date: 2014-09-19
Publication date: 2015-03-26
Also published as: DE102013015564A1; US20160236326A1; EP3046728A1; CN105592983A

Abstract

The invention relates to an abrasive medium which is bonded with a thermosetting material and comprises abrasive particles, a thermosetting binder and optionally further fillers, and contains a phosphate-based additive, the percentage of the phosphate-based additive being 1 to 10 wt.-% of the starting mixture of the abrasive medium. The phosphate-based additive is homogeneously distributed in the abrasive medium. The invention also relates to a method for producing corresponding thermosetting resin-bonded grinding disks.

Description

Abrasive with phosphate-based filler

The present invention relates to thermoset bonded abrasives consisting of a mixture of abrasive grain, thermosetting binder and optionally further fillers, and a method for producing corresponding thermoset bonded grinding wheels.

The duropastically bonded abrasives of the present application may be thermoset bonded abrasive wheels or other abrasives, such as coated abrasives.

A grinding wheel consists essentially of abrasive grain, which is pressed with a binder to a grinding wheel. Duroplastics, in particular phenolic resins, modified phenolic resins, e.g. Epoxy and / or rubber modified phenolic resins used. In addition, a grinding wheel may contain other fillers. These may be abrasive (e.g., cooling), thus assisting the grinding process or serving to stabilize (burst resistance, flexibility) the grinding wheel.

Abrasive materials also consist essentially of abrasive grain and binder. However, this abrasive mixture is not pressed into a self-supporting body, but is applied as a thin layer to a support material such as paper, fabric or plastic. For this purpose, a binder layer used as an adhesive layer is first applied to the carrier. Subsequently, the abrasive grain is usually applied under the action of an electric field directed to the adhesive layer. To stabilize the abrasive grain is then coated with a second binder layer.

EP 0 855 948 relates to abrasives such as grinding wheels coated with a phosphate-containing coating. The grinding wheels can be, for example, resin-bonded grinding wheels, which essentially consist of abrasive grain, which is shaped together with a binder into a grinding wheel. The coating also consists of a binder in which a hydrogen-free inorganic Metal phosphate salt is dissolved. The phosphate additive is therefore contained exclusively in the outer surface of the grinding wheel. The grinding wheels provide useful grinding performance on metal surfaces, such as titanium, with reduced energy consumption.

DE 2 324 222 relates to a ceramic bonded grinding wheel, wherein the ceramic binder is provided with a Phosphatzusatz. Phosphates are often added to ceramics to reduce the curing temperature of the ceramics. In addition, the addition of 10 to 20 wt .-% of alkali or alkaline earth metal phosphates to the ceramic binder, the adhesion of the binder on the abrasive grain, and the mechanical strength of the grinding tool is increased. The grinding wheels are cured at temperatures of up to 1280 ° C.

WO 2010/040472 A2 relates to ceramic-bonded abrasive grain agglomerates. The binder essentially contains aluminosilicate, water glass and water. The binder mixture may also contain inorganic phosphates and other grinding aids or fillers. To prepare the abrasive grain agglomerates, the abrasive grain is mixed with the binder, wherein primary particles are assembled to form abrasive grain agglomerates. The abrasive grain agglomerates are then dried and cured at temperatures up to 400 ° C.

It is generally known in the abrasives industry that abrasives, in particular grinding wheels, are subject to certain aging effects. One cause of these aging effects appears to be the adsorption of moisture by the material of the grinding wheel. In the process, according to today's understanding, the interface between the grain and the surrounding binding matrix is weakened by moisture diffusion, which leads to an easier breaking away of the abrasive grain. These phenomena are enhanced by alkaline-reacting binding components which contribute to decomposition of the phenolic resin matrix. The life of conventional grinding wheels is significantly affected by these aging effects.

Previous studies (C. Stang; "Formulation and humidity influences on the lifetime of phenolic resin-bonded cut-off wheels, Chair of Plastics Technology 2009, Erlangen and investigations at Rhodius Schleifwerkzeuge GmbH) have shown that grinding wheels usually after a storage time of 8 to 12 months with respect to bound in the matrix Moist a saturated equilibrium reach with their surroundings. This corresponds to a conditioning period of 14 to 21 days in a humid climate according to DIN 50016. On the basis of a standardized test method, the determined grinding wheel performance alone goes back to about 40% to 50% of the initial power due to these aging effects, the power loss initially being significantly greater and the curve flattening towards the saturation point.

The aging effects seem to be relatively independent of the resin systems and grain coatings used. In extensive series of tests, conventional modifications of the resin systems, the grain coatings and various abrasive fillers have not been able to achieve any positive effects with regard to extending the service life or maintaining the performance of the grinding wheels.

So far, it is attempted to prevent aging phenomena in grinding wheels by suitable packaging, for example by welding grinding wheels in plastic films. However, aging effects can of course only be prevented as long as the packaging is closed. If the packages are opened or the diffusion barriers of the packages are exceeded for a sufficient period of time, aging effects can not be prevented. Reclosable, diffusion-tight packaging, in contrast, are comparatively complicated and expensive.

The object of the present invention is to provide an abrasive with a longer service life and higher grinding performance, without significantly increasing the production costs and without complicating the handling of the abrasives.

This object is achieved in that the abrasive of the type mentioned a phosphate-based additive is added. The phosphate-based additive is contained in the starting mixture of the abrasive in a concentration of 1 to 10% by weight and distributed homogeneously in the abrasive.

In a preferred embodiment, the phosphate-based additive is contained in the starting mixture of the abrasive in a concentration of 1 to 5 wt%, and preferably in a concentration of about 4 wt%. In a further preferred embodiment, the proportion of the phosphate-based additive is 2 to 10% by weight, preferably 5 to 7% by weight, of the weight fraction of the abrasive grain contained in the starting mixture.

Preferably, the phosphate-based additive contains phosphates of alkaline earth metals, such as magnesium, calcium, strontium and barium phosphates, iron (II) phosphates, iron (III) phosphates, manganese, aluminum and zinc phosphates, synthetic or mineral phosphates, and Mixtures thereof. The phosphate-based additive is particularly preferably a calcium phosphate such as dicalcium phosphate or its anhydride or monetite or brushite, tricalcium phosphate or hydroxyapatite or pentacalcium hydroxytriphosphate (CasiPO.sub.OH, fluorapatite, dimagnesium phosphate, trimagnesium phosphate, magnesium diphosphate or a mixture thereof the phosphate-based additive is insoluble in water and is not subject to any chemical or physical change in the manufacture of the abrasive.

As binders, any thermosets are used in the abrasive of the present invention. Preferably, synthetic resins such as phenolic resins or modified phenolic resins, e.g. Epoxy- and / or rubber-modified phenolic resins used as binders.

Preferably, the proportion of the binder is 1 to 40 wt .-%, preferably 5 to 30 wt .-% and particularly preferably 10 to 20 wt .-% in the starting mixture of the abrasive.

As fillers, sodium cryolite, potassium cryolite, potassium aluminum fluorides, iron sulfides, zinc sulfides, manganese sulfides, manganese chlorides, copper sulfides, chalcopyrites, pyrroles, iron (II) oxides, iron (III) oxides, iron (II / III) oxides, lime, chalk, carbon modifications such Graphite, carbon black, coal, and mixtures thereof are used.

Tricalcium phosphate (TCP) has hitherto been used, for example, in food technology as an acidity regulator, setting agent or release agent. It is also used as a so-called "anti-caking agent" to counteract the agglomeration of moisture-sensitive bulk solids, whereby the concentrations used are usually in the single-digit percentage range. As a result of the large specific surface area (up to 70 m ² / g) of the powder particles it is possible to reversibly adsorb more than 10% moisture based on the weight of the particles on the particle surface.

Extensive experiments have shown that the addition of a phosphate-based additive increases both the service life and the performance of the inventive abrasives. Apparently, the phosphate additive prevents the bonds between the abrasive grain and the binder from being attacked and affected by the ingress of moisture.

It is known that e.g. TCP has good moisture adsorption capacity. However, since the moisture can only be adsorbed latently and reversibly by TCP, it was not expected by those skilled in the art that the addition of such a phosphate-based additive would increase the life of resin-bonded abrasives. In particular, it was not to be expected, and so far can not be explained exactly, which leads to an increase in the grinding performance of the abrasives according to the invention.

Another advantage of the abrasives of the present invention is that the phosphate additive does not undergo any physical or chemical change during abrasive production. Therefore, clearly crystalline apatite phases can be detected by means of X-ray diffraction in ashing residues of abrasives. In addition, by means of X-ray fluorescence spectrometry, the proportion of phosphate in the residue of the residue can be precisely quantified and thus the phosphate content of the underlying abrasive composition can be calculated.

The abrasives of the present invention may be abrasive wheels, coated abrasives or any other abrasive. In the case of coated abrasives, the percentages by weight used here are based on the weight of the starting material (abrasive grain, binder, additives) of the abrasive. The weight of the pad is not added to the weight of the starting mixture.

The subject matter of the present application is also a process for the production of a grinding wheel with a phosphate-based additive, the additive being based on phosphorus. phosphate base contained in the starting mixture of the grinding wheel in a concentration of 1 to 10 wt .-% and is homogeneously distributed in the abrasive. The method comprises the steps of providing a phosphate-based powder additive, mixing the powdery phosphate-based additive with abrasive grain, binder and optionally further fillers, filling the starting mixture into a designated mold, adding glass cloth, compressing the mixture to a green compact and the curing of the green compact to obtain a grinding wheel.

Preferably, in the method for producing a grinding wheel according to the invention, the powdery phosphate-based additive is first mixed with the abrasive grain. Subsequently, this mixture is mixed with the binder and optionally further fillers. Due to the intensive mixing, the phosphate additive is homogeneously distributed both in the starting mixture and in the finished grinding wheel.

The production of a coated abrasive article according to the invention essentially corresponds to the production of conventional coated abrasives. It should only be noted that a homogeneous distribution of the additive is achieved in the abrasive. In particular, if the abrasive grain is applied electrostatically to the substrate, it may be advantageous to mix the additive with the binder of the adhesive layer and the cover layer to ensure a homogeneous distribution of the additive in the abrasive.

With reference to the following figures, the abrasives of the present invention and the process for their preparation are discussed in more detail. Show it:

1 shows a diagram of the normalized power values of the grinding wheels according to Examples 1 and 2 and the reference disk 1 in the automatic test;

FIG. 2 is a graph of the normalized power values of the grinding wheels from FIG. 1 in the hand test; FIG.

Fig. 3 Diagram of the normalized power values of the grinding wheels according to Example 3 and the reference disk 3 in the hand test. Fig. 4 Diagram of the normalized power values of the grinding wheels according to Example 4 and the reference disk 1 in the hand test.

Production of grinding wheels:

To illustrate the advantageous properties of the abrasive according to the invention, the grinding performance of grinding wheels with phosphate additives with the

Abrasive performance of conventionally made phenolic grinding wheels compared. Table 1 gives an overview of the examined grinding wheels.

Table 1: Examined grinding wheels

The grinding wheels according to Examples 1 and 2 (test No. 13290.1 and 13290.2) contain 65% by weight of corundum abrasive grain with a grain size of F46 and F60. The abrasive grain was first mixed with 4 wt .-% feinpulvrigem TCP with a particle size D50 (equivalent to 3 to 5 μηη). Subsequently, 7.5% by weight of liquid phenolic resin was added to the mixture. Finally, this mixture was added to a template of 10.5 wt .-% powdered phenolic resin and active fillers, namely 10 wt .-% cryolite and 3 wt .-% potassium aluminum fluorides and mixed intensively by means of an Eirich Intensive Mixer for 30 minutes. The granulated starting mixture thus prepared was sieved with a sieve of 2 mm mesh to to remove larger chunks. The granules were then weighed out into molds, glass cloths, labels and flange rings added and pressed into green compacts. The green compacts were last cured at an elevated temperature of 185 ° C for a total of 18 hours. The grinding wheels according to Example 1, 2, 4 and according to Reference 1 have a radius of 125 mm and a thickness of 1 mm.

The reference grinding wheels 1 and 3 were made by the same method, these reference wheels were of course made without the addition of TCP. Instead, these discs contained correspondingly more fillers.

For the grinding wheel according to Example 2, the same components were used as in the grinding wheel according to Example 1. However, in the grinding wheel according to Example 2, the manufacturing process was slightly modified. The TCP was not added to the abrasive grain, but to the mixture of powdered phenolic resins and active fillers.

The grinding wheel of Example 4 was also made substantially like the grinding wheel of Example 1. However, in the grinding wheel according to Example 4, a different phosphate additive, namely dicalcium phosphate anhydride (CaHP04) was used. DCP Anhydride is also called Monocalciumhydrogenphosphat and occurs in natural form as Monetit or Brushit.

The grinding wheels according to Example 3 and Reference 3 have a format of

230 x 1, 9 mm.

Investigation of the grinding performance of the grinding wheels:

To analyze the grinding performance of the grinding wheels, the grinding wheels were subjected to standardized performance tests, namely an automatic test and a hand test. The grinding wheels went through all the same grinding test program.

The test machine used in the automatic test consists of a device in which an angle grinder (Flex, 1400W) is clamped to a movable arm and the arm is moved up and down by a motor with fixed feed. During the downward movement, an approximately 2 to 3 mm wide piece of a steel tube is res (V2A 15x15x1, 5 mm) separated. After the upward movement of the tube is nachgeschoben with an automatic device, so that in the next downward movement again a piece of pipe is separated. The machine permanently determines the remaining diameter of the disk and counts the separation processes. With a residual diameter of the grinding wheel of 95 mm, the machine stops the attempt.

In the hand test the angle grinder (Flex, 1400W) was guided by a test person. In each case, a predetermined number of cuts were made in V2A solid material. The solid material (square rod V2A, 25x25 mm) was firmly clamped in a vise. The grinding performance was determined by comparing the grinding wheel diameter before and after the test. The determined disc abrasion represents a measure of the grinding performance.

FIG. 1 shows the results of an automatic test on pipe V2A 15 × 15 × 1.5 mm for the grinding wheels according to Examples 1 and 2 and Reference 1.

For some of the grinding wheels, the grinding test was carried out immediately after production. At this time, the grinding performance of the grinding wheels is maximum. In order to investigate the influence of moisture on the grinding performance, the other part of the grinding wheels was suspended individually suspended in a climate chamber and exposed to a humidity change climate according to DIN 50016. The storage in such a climatic chamber over 14 to 21 days corresponds approximately to the storage of the grinding wheels under normal conditions Central European climate over 8 to 12 months. As discussed above, after this storage time, phenolic resin bonded abrasive wheels have typically reached equilibrium with respect to the moisture bound in the wheel material and the grinding performance reaches a saturation level.

After various storage times of 3, 7, 14 and 21 days, test sets of the grinding wheels were removed and also subjected to the grinding test program. In FIG. 1, the standardized power values are plotted against the storage time. The grinding wheels tested directly after production (storage time: 0 days) showed the highest grinding performance. The number of cuts that could be made with these wheels was normalized to 100%. As can be seen from FIG. 1, the grinding performance, ie the number of cuts made, of the reference grinding wheel 1 with the storage time continuously and approximates after 21 days of storage to a grinding power level of about 50% of the original power. The grinding performance of the grinding wheels according to Example 1 and 2 also decreases with increasing storage time. However, the experiments clearly show that the decrease in the grinding performance is lower and that the saturation grinding power reached after 21 days of storage is over 60% higher than the saturated grinding performance of the conventionally produced reference grinding wheel 1.

Surprisingly, the grinding wheel according to Example 1 showed a further advantageous effect. The grinding wheel according to Example 1 had a higher initial grinding performance compared to the reference grinding wheel 1. The grinding wheel according to Example 1, which was tested directly after its production, performed 237 cuts until a residual diameter of 95 mm was reached. With the reference grinding wheel 1, however, were only

208 cuts possible. This corresponds to an increase in performance of the grinding wheel according to the invention compared to the reference grinding wheel 1 of about 14%.

A grinding wheel from a repeat experiment of Example 1 described above (Experiment No. 13290.3) showed an initial performance of 241 cuts on pipe V2A 15x15x1, 5 mm in the automatic test. To examine the saturation grinding performance, this disc was left in the climatic chamber for 69 days (2 months and 1 week). The normalized residual power was still 59% of the initial power (141 cuts in the automatic test on tube V2A 15x15x1, 5 mm) even after this long exposure in alternating climate. This shows that the grinding performance, which occurs after 21 days in the alternating climate, actually represents a saturation grinding performance and that even after longer residence times no significant change in the grinding performance due to the storage conditions more occurs.

Interestingly, with a grinding wheel according to Example 2 only 189 cuts could be made. The initial power of the grinding wheel according to Example 2 was thus 10% lower than the initial power of the conventional disk. The reason for this is evidently the type of incorporation of the TCP additive in the production of grinding wheels. While the grinding wheels of Examples 1 and 2 each have markedly improved performance retention characteristics over conventional grinding wheels, only the grinding wheel of Example 1 provides the added benefit of increased initial grinding performance. FIG. 2 shows the normalized power values of the grinding wheels from FIG. 1 in the hand test on solid material V2A 25 × 25 mm. In this test, 10 cuts were made and then the remaining diameter of the grinding wheels was determined. Qualitatively, the results agree with the findings of the automaton test described with reference to FIG. Also in the hand test it turned out that the

Grinding performance of the grinding wheels according to Example 1 and 2 is generally higher than the grinding performance of the reference grinding wheel. 1 In particular, the results after 21 days storage show that the saturation grinding power of the reference grinding wheel 1 is slightly less than 50%, whereas the saturation grinding power of the grinding wheels of Examples 1 and 2 is still approximately 60% of the initial power.

The slightly fluctuating results in the results of the hand test are probably due to the removal times of the grinding wheels from the climatic chamber. Since (in particular) at storage times of less than 21 days, if necessary, no saturation of the moisture absorption has occurred, here is the

The grinding performance is believed to be affected by the moisture prevailing at the time of removal of the wheels. On the other hand, the daily form of the test person must also be taken into account.

In the diagram of Figure 3, the results of the performance test for grinding wheels according to Example 3 and reference grinding wheels 3 are shown. In this experiment, the performance and the aging of the grinding wheels was determined by means of a hand test on solid material V2A 25 x25 mm. Here, 20 cuts were made with each grinding wheel and the disc abrasion determined by measuring the wheel diameter before and after the test. The results again show the positive influence of the TCP additive on the performance of the grinding wheels. In addition, with the reference disc 3 only 21 more cuts could be made after 21 days of storage, the remaining diameter permitted no further cutting in the solid material V2A 25 x 25 mm. As shown in FIG. 3, with the conventional grinding wheel after 21 days of storage, only a grinding performance of less than 15%, taking into account the missing cut, could be achieved compared to the initial grinding performance. In contrast, the grinding performance of the grinding wheel according to Example 3 reached a saturation grinding power of about 50% after 21 days. In addition, this experiment again shows that the initial grinding performance, ie the grinding performance directly after production (storage: 0 days) of the grinding wheel according to the invention is higher than the initial grinding performance of the reference grinding wheel 3. In the grinding wheel according to Example 3, the abrasion after 20 was Cut only 15.7 mm, while the abrasion of the reference grinding wheel 3 was 16.2 mm. This is all the more astonishing since the reference grinding wheel has 4% by weight more abrasive grain than the grinding wheel according to Example 3 and therefore a higher initial power of the reference grinding wheel was to be expected. Since the initial grinding performance is not yet influenced by any moisture absorption of the grinding wheel material, the improved grinding performance can not be explained solely by the adsorptive properties of the TCP additive. Rather, there must be other effects due to which the TCP additively increases the grinding power of synthetic resin grinding wheels.

The same performance tests were carried out for grinding wheels according to Example 4. As stated above, the formulation of these grinding wheels corresponds to the recipe of the grinding wheels according to Example 1 with the difference that DCP anhydride was used instead of TCP. The DCP was also added to the abrasive grain. The initial grinding performance of the grinding wheels according to example 4 was 258 cuts in the automatic test, thus again higher than the initial power of the grinding wheels according to the previous examples. However, the automatic test on V2A tube 15x15x1, 5 mm did not show a significant positive effect after 14 days of aging. The determined residual power in this test was 52% of the initial power.

In the diagram of Figure 4, the results of the performance test for grinding wheels according to Example 4 are shown. The reference disc corresponds to the reference disc from Figure 2. In the hand test (10 sections on solid material V2A 25x25 mm), the normalized power, however, after 7 days at 78% of the initial power was significantly higher than the reference with 56% remaining power at this time. After 14 days of aging, the residual power of 66% was still significantly above the residual power of the reference 32%. At the time of registration, this test series was not yet completed, so that no information on the grinding performance of the grinding wheels according to Example 4 after

21 days can be made. The preceding examples relate exclusively to resin-bonded grinding wheels. However, it can be assumed that the beneficial effects of the phosphate additive also occur with all other thermoset bonded abrasives, such as abrasives on backing.

Claims

claims

1 . A thermoset bonded abrasive comprising abrasive grain, thermosetting binder and optionally further fillers,

characterized in that

the abrasive contains a phosphate-based additive, wherein the amount of the phosphate-based additive is from 1 to 10 percent by weight of the starting mixture of the abrasive and wherein the phosphate-based additive is homogeneously dispersed in the abrasive.

2. An abrasive according to claim 1, wherein the proportion of the phosphate-based additive in the starting mixture of the abrasive is from 1 to 5% by weight, and more preferably about 4% by weight.

3. An abrasive according to claim 1 or 2, wherein the phosphate-based additive comprises phosphates of alkaline earth metals, such as magnesium, calcium, strontium and barium phosphates, iron (II) phosphates, iron (III) phosphates, manganese, Aluminum and zinc phosphate, synthetic or mineral phosphates, and mixtures thereof.

4. An abrasive according to any one of claims 1 to 3, wherein the phosphate-based additive is a calcium phosphate such as dicalcium phosphate, tricalcium phosphate, hydroxyapatite, fluorapatite, dimagnesium phosphate, trimagnesium phosphate, magnesium diphosphate or mixtures thereof.

5. An abrasive according to any one of claims 1 to 4, wherein the phosphate-based additive is water-insoluble.

An abrasive according to any one of claims 1 to 5, wherein the binder is phenolic resin or modified phenolic resin.

7. An abrasive according to any one of claims 1 to 6, wherein the proportion of the binder is 1 to 40 wt .-%, preferably 5 to 30 wt .-% and particularly preferably 10 to 20 wt .-% of the starting mixture of the abrasive.

8. An abrasive according to any one of claims 1 to 7, wherein the abrasive is an abrasive disc or a coated abrasive.

9. A method of making a thermoset bonded abrasive wheel comprising the steps of:

Providing phosphate-based powder additive, wherein the proportion of the phosphate-based additive is 1 to 10% by weight of the starting mixture of the grinding wheel,

- Mixing the powdery phosphate-based additive with abrasive grain, binder and optionally other fillers, so that the phosphate-based additive is homogeneously distributed in the starting mixture.

- filling the starting mixture into a designated mold;

- addition of glass fabric;

- Pressing the mixture into a green compact;

- Hardening of the green body to obtain a grinding wheel.

10. A method for producing a grinding wheel according to claim 10, wherein the powdery phosphate-based additive is first mixed with the abrasive grain and this mixture is then mixed with the binder and optionally further fillers.