DE3126158A1 - METHOD FOR PRODUCING GRINDING WHEELS BINDED WITH PHENOL RESIN - Google Patents

Description

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1A-54,698

Note: Norton Co.

description

Process for the production of

phenolic resin bonded grinding wheels

The invention relates to grinding wheels with a phenolic resin bond which are hardened with the aid of hexamethylenetetram has been, in particular grinding and cutting discs, and a method for their production.

In the manufacture of resin-bonded grinding wheels or, more generally speaking, grinding wheels, a certain amount of abrasive grain mixed with phenolic resin powder, the mixture molded and then the resin hardened. In order to improve the resin absorption of the abrasive grain and the binding force of the resin, one can Moisten the abrasive grain with furfural before mixing it with the resin or the binding material (U.S. Patent 3,406,020 and British Patent 1,207,766). After US Pat. No. 3,406,020 phenolic resin bonded abrasive articles with various additives are made by Mixing of abrasive grit and binding compound, which is said to result in improved flexural strength. Different Types of abrasive grain such as alumina, corundum, silicon carbide and diamond can be produced with the help of a novolak resin, which is provided with hexamethylenetetramine as a hardener. The hardener comes in a lot of about 2 to 50% by weight, based on novolak, preferably about 3 to 20, in particular 7 to 15%, are used. According to this prior art, 0 to about 100 parts of a wetting agent can be used per 100 parts of novolak, wherein the wetting agent can be a liquid resol, cresol, furfurol or furfuryl alcohol. The wetting

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Medium is used with the abrasive grit in such quantities mixed that about 40 parts of wetting agent to 80 parts of novolak binder or 10 to 20 parts of furfural come to 120 parts of novolak resin. The recipe is set so that the mixture of abrasive grain, Wetting agent and binder at room temperature, is free flowing and the only criterion is it determine how much wetting agent one can apply to keep the mixture up relatively free flowing remains at the moment when it is filled into the mold.

GB-PS 1 207 766 relates to the production of improved self-sharpening manually adjusted grinding discs for use in foundries, the pore volume of which is 22 to 26 % and the abrasive grain is spinel and / or mullite. The manufacture of abrasive articles of such porosity and of abrasive grain and resin bond is described with mention of the use of furfural. There is only one indication, however, and that is that furfural is used in the usual way as a plasticizer in an amount of 122 cnr / kg dry resin binder. It is not about the use of hexamethylenetetramine.

The invention now relates to abrasive bodies, in particular Roughing and cutting wheels, where the relationship between the amount used as a wetting agent of furfural to the amount of hardener for the binder resin matters.

In the term "mixture" used here, as usual, a more or less granular mixture of Abrasive grain coated with powdery non-hardened Understood polymers or resins. The terms

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"Bond" or "resin bond" includes application of only resin as well as resin and one or more fillers, grinding aids, reinforcing agents and the like as usual.

It has been found that a maximum grinding ratio for a given grinding wheel is much safer to achieve If a preferred amount of furfural as a wetting agent is applied to the abrasive grain is applied before mixing with the powdery resin binder. Furfural is used for wetting of the abrasive grain and is used in a certain amount with regard to the hardener hexamethylenetetramine added, which in turn is introduced into the resin binder in a special amount in order to achieve the Adjust the service life of the grinding wheels.

It is known that the service life of grinding wheels bonded with phenolic resins, such as grinding wheels or cutting wheels, can be improved by increasing the crosslinking density of the phenolic resin by increasing the amount of hardener in the novolak resin. Now it has been found in addition that a unique relationship between the amount of furfural as a wetting agent which is applied to the abrasive grain _f and the amount of hardener, which the novolac resin is added exists. The amount of wetting agent can be varied in order to adjust the grinding behavior of the grinding wheels as required.

the production of the object of the invention is / in terms of service life and grinding behavior of improved grinding tools, in particular grinding wheels such as grinding and cutting wheels, with maximum grinding ratio at a certain composition, with a certain amount of furfural

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for wetting the abrasive grain and a certain Amount of hexamethylenetetramine is used as hardener for the resin binder and the proportions of furfural and hexamethylenetetramine have a certain relationship to one another.

The attached diagram shows the dependency of the grinding ratio of the grinding wheel according to the invention on the amount of furfural as a function of the amount of hexamethylenetetramine.

The following is the grinding wheel according to the invention on the preferred embodiment, namely a Növolak resin as a binder further explained. It is about it is a phenol-formaldehyde condensation product, but other phenol resins such as modified ones can also be used Phenol-formaldehyde resins, phenol-furfural resins or the like can be applied. The term "phenolic resin" includes the hexamethylenetetramine curable resins.

Common resin-bonded abrasives include grinding wheels for a wide variety of grinding processes, such as cutting wheels, Stick grinding disks and grinding disks for GJäBereitechnik, especially for Machining of turning steels, production of steel billets for rolling and for the most diverse Grinding operations in the foundry. Most for this Grinding wheels used for purposes are hardened with hexamethylenetetramine Novolak resins produced as binders in order to obtain good hardening bonds and good service life of the panes. It is known, that the amount of hardener has a direct influence on the service life of the grinding wheel, since the crosslinking density of the wheel bond largely depends on the application of more or less hardener. So far, however, no relationship has been established between the tool life and

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the amount of furfural at the same time as the amount of hardener known for the novolak resin.

It has been found that the grinding ratio of a wheel, i.e. the amount of material used by a Workpiece removed per volume unit of grinding wheel can be optimized for any phenolic resin binder by using optimal amounts of furfural to wet the abrasive grain before it is mixed with the binder, the amount of furfural is related to the amount of hardener for the resin. Until now, furfural was used to wet the abrasive grain before mixing with the powdered novolak resin and if necessary fillers are used, the dimensioning of the wetting agent has not yet been carried out in With regard to the amount of hardener used. In particular, it was not known that the grinding ratio of the The grinding wheel is adjustable by varying the amount of furfural for wetting the grinding body, wherein the amount of furfural depends on the amount of hexamethylenetetramine as hardener for the novolak resin.

With reference to the diagram it can be said that when using furfural as a wetting agent for the abrasive grain for with novolak resins, hardenable

Grinding tools

With hexamethylenetetramine, hard-wearing grinding ratios can be achieved if 9 to 14 % hexamethylenetetramine and 44.5 to 133.3 cnr / kg furfural - based on phenolic resin - are used for wetting the abrasive grain in the resin bond. The diagram shows that with increasing amount of furfural compared to increasing amount of hexamethylenetetramine in the novolak binder, the grinding ratio in the abrasive article produced in this way is optimized. Within the range of 9 to 14 % hardener in the resin binder there is an optimal furfural value for wetting

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of the abrasive grain must be observed in order to match the grinding ratio of the hardened grinding wheel with a to keep the special phenol-resin bond as high as possible. According to the invention, the phenolic-resin bond for a given abrasive grain for the production of a grinding wheel with the desired service life that more or less hardener and appropriate amounts of furfural for optimal sanding properties Disc can be achieved.

In order to show the advantage of the relationship between the amounts of wetting agent and hardener, two grinding disks for steel processing made of Al ₂ O * / ZrO ₂ abrasive grain, grain size about 1.2 mm _} with the phenolic resin commonly used were used for very dense Slices made. The abrasive grain for each disc was wetted with furfural prior to mixing with the novolak resin, which contained 14 % hexamethylenetetramine as hardener, for one disc with 37.8 cär / kg resin and for the other with 89 cnP / kg resin . The mixture was hot-pressed and the resin cured in a conventional manner. The test disks produced in this way had a diameter of 406 mm, a thickness of 51 mm and a center hole with a diameter of 152 mm. The disks were each clamped on a 30 HP roughing machine and a low-alloy steel of the specification AISI 4140 was machined with a head force of 180 kg and a circumferential speed of about 48.5 m / s. The disk wear and the metal removal as well as the force required to drive the disk were determined. The following results were achieved:

a) The disc, produced using the lower amount of furfural (first disc ) _t showed a wear of 418 cnr / h, a material removal of 52.5 kg / h

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a power consumption of 20.4 kW and thus a grinding ratio of 4.57 (25.51 cb.in / h, 116.6 lb / h);

Id) the corresponding values for the disc with higher Furfural content (second wheel) were 341 cnr / h, 50 kg / h, 18.88 kW and the much better grinding ratio 5.34 (20.82 cb.in / h, 111.13 lb / h).

These results show the better grinding ratio the disk 2 compared to the disk 1 with 14% hexamethylenetetramine (see diagram above curve). With the first disc you get roughly the same Material removal, but less force is required with the second disc.

For some grinding wheel recipes, high amounts of furfural can be added to the abrasive grain during mixing are not added or mixtures are obtained which cannot be handled or can only be handled with difficulty. To overcome this problem, a partial amount of furfural is added directly to the abrasive grain and * the Remainder alone or mixed with a second liquid after the abrasive grain has been introduced into the Binder added to the whole.

The invention is further illustrated by the following example.

example

Hot-pressed cutting discs with a novolak binder and 9 % hexamethylenetetramine as hardener were produced. Two disks contained clay as abrasive grain, grain size 0.71 mm, disk diameter 610 mm, thickness 4.76 mm, center bore 44.5 mm. When making the first

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Disc were applied 15 car furfural for the wetting of the abrasive grain and then a further amount of furfural was added to the mixture, so that finally a total of 124 cnr furfural, relative to 1 kg of resin ^ templates.

When producing the second disc, 30 cm were used to wet the abrasive grain and the total amount of furfural was set to 155.5 car .

Various tests were carried out with these two disks. Served to drive the discs a dry grinding machine "Tabor Hydraulic Chop machine", with a running speed of 2,200 rpm. It should be round bars with a diameter of 50 mm can be separated from a corrosion-resistant steel of specification 304. It took 6 s for each cut. The average grind ratio for the first Disc was 3.21 and for the second disc it was 2.50 (see diagram below curve).

In another experiment, these cutting wheels were run on plunge-cut loops at 20 kW for a Fox pendulum grinding machine examined and that took place a 50nmin penetration into a steel of specification C1018CR at 1,900 rpm. When trying it turned out for the first wheel a grinding ratio of 0.99 and for the second wheel 0.86.

This confirms that with the same force absorption of different cutting discs from different amounts of furfural in relation to the amount of hexamethylenetetramine, higher grinding ratios are obtained with a lower furfural content and 9 % hexamethylenetetramine, which confirms the dependence of the amount of furfural on the amount of hardener.

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Various difficult tests can be carried out in the laboratory under regulated conditions, to be able to compare the relative strength of the resin bond of the disc. For this purpose rods Contains the same abrasive grain and the same resin bond with a standardized composition shaped and - as for trimming or grinding discs common and described above-hardened. It then becomes the flexural strength of each hardened rod with 3-point support and a distance of 50 mm with Determined using an Instron testing machine to determine the mean force required to break. This flex test shows that the disc strength is retained even when the amount of furfural is used to optimize the grinding ratio while extending the service life is changed, as is results from the following values.

A number of 127 x 12.7 ^# 6.35mm alumina rods Zirconia - abrasive grain, 0.71mm grit with a modified resin bond - containing "Carbosota" as a wetting agent and phenolic resin powder in an amount of about 44.5 cm ^ / kg. In these bars, the abrasive grain was bonded with novolak resin using 9 and 14% hexamethylenetetramine and 37.8, 89 and 133 cnr / kg furfural, respectively.

-% wt .-%

Abrasive grit 54

Resin bond 46

100 100

The hardened rods were examined for the mean force to break of 4 rods. The average strength of the bars with the lowest

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Furfural amount was 9,998, with medium furfural ^ content 10 626 and for the highest furfural content 9 763 N / cm (14 490, 15 400 and 14 150 psi). This results in, that the pane strength remains high when large amounts of hexamethylenetetramine are added. The addition of furfural to the abrasive grain during mixing in relation to the amount of hardener does not affect the strength of the bond with increasing hardener content.

The determination that the ideal amount of furfural for the abrasive grain is related to the amount of hardener of the bond y is essential as this helps to improve the service life and the grinding ratio of modern grinding wheels, which is desirable in view of the industrial introduction of new grinding wheels for machining steels with higher power consumption. When these heavier machines are used at full capacity for roughing steel billets, the aim is to achieve maximum wheel life. The grinding wheels according to the invention have a longer service life than the known ones, and this advantage can be attributed to the corresponding adjustment of the amount of furfural to the amount of hexamethylenetetramine.

It has generally been observed that certain combinations of amounts of furfural with hardener in novolak resins of the bond have an influence on the grinding ratio, the service life and the strength of the grinding wheels. If the hexamethylenetetramine amounts are above 12% by weight, based on resin, and go up to 20 % , the amount of furfural should be increased proportionally from 44.5 to 133 cnr / kg resin. Grinding wheels with own

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shafts of the discs according to the invention are so far produced by adding additives such as fillers, grinding aids and the like to the mixtures, hot or cold pressing and then the binder is hardened.

A wide variety of products can be used as abrasive grain for the abrasive bodies according to the invention, such as fused and sintered clay, fused and sintered Al ₂ 0 ₃ -Zr0 ₂ , silicon carbide, spinel, flint, mullite, cubic boron nitride, boron carbide, diamond and mixtures thereof.

Claims (1)

DRINK. FRANZ VUESTHOFF PATENT LAWYERS 'Z' - ■ '': . _Λ ...... -. DR. PHIL. PREDA * UESTHOFF (I9I7-I9J6) WUESTHOFF-v.PECHMANN-BEHRENS-GOETZ d, pl .-, ng.gbrhard puls < _W 2- _W x) DIPL.-CHEM. DR. E. BARBER OF PECHMANN PROFESSIONAL REPRESENTATIVES BEFORE THE EUROPEAN PATENT OFFICE DR.-ING. DIETER BEHRENS MANDATAIRES AGREES PRES l'OFFICE EUROPEEN DES BREVETS DIPL.-ING .; DIPL.-VIRTSCH.-ING. RUPERT G0BT2 1A-54 698 D-8000 MUNICH Annui Norton Co. Schweigerstrasse 2 • TELEPHONE: (089) ^ 62051 'TELEGRAM: PROTECTPATENT TELEX: J 24 070 Claims 1. Process for the preparation of resin-bonded hexamethylenetetramine-cured ones Abrasive body improved grinding ratio and longer service life, characterized in that the abrasive grain wetted with furfural and this then with the binder resin containing hexamethylenetetramine as hardener mixes, and optionally a further amount of furfural added to the mixture / and then processed the mixture in a known manner to form the abrasive article, wherein the total amount of furfural between 44.5 and 133 cm * / kg resin depending on the amount of hardeners that is between 12 and 20 wt .-%, based on resin, is measured. Process according to Claim 1, characterized in that a novolak resin is used as the binder resin used. 5. The method according to claim 1 or 2, characterized ge mark ze ichnet that to 14 wt .-% hexamethylenetetramine - based on resin - 89 approx? Furfural used per cm resin. 8146