DE1805290A1 - Electrically conductive abrasives and processes for their manufacture - Google Patents

Description

Electrically conductive abrasives and processes for their Manufacture «

Electrically conductive grinding bodies are known in which metal powders are bonded with the aid of a phenol-aldehyde resin and are intended to be used for electrolytic grinding. In the case of the known grinding bodies, in particular grinding wheels, the minimum metal content should be 38 % by volume and can amount to about 59% by volume. In such grinding wheels the volume ratio of binder to metal is about 0.7 to 1.7. Resin-bonded grinding wheels are also known in which k-0 to k $ vol .- $ metal are present, that is, corresponding to a binder to metal ratio of about 0.7 to 3.

In these well-known products, the ratio of binder to metal is lower than would be desirable «, The metal content has a detrimental effect on the physical properties of the bond. The grinding tools can only

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worked hard on tolerance, so that already out of these Reason a lower iietall share would be desirable.

The invention now brings grinding bodies, in particular grinding wheels, which contain silver as metal powder, whereby- eier Ke-. The metal content is only about 1/5 of the tightness that was previously required for sufficient electrical properties of the grinding wheel. .. xairden deemed necessary for electrochemical grinding .. No distinction was made with the known products · .with regard to the type of metal, i.e. copper or silver. The fact that the resistance of silver is about $ 6 lower than that of copper is ignored (1.6.10 " ⁰ Jr. era for silver versus 1.7.1C ™ Si» cm for copper In the case of the grinding wheels according to the invention, the silver content should amount to Ij to 25 vol .-, J of the binder.

The proportion of abrasive grain can vary between wide limits vary. Ilan can use common abrasive materials. Because it in the field of application of the abrasive articles according to the invention ur: i is a pure electrochemical grinding "so is actually the task of the abrasive grain is only a subordinate one. It should give the workpiece the desired tolerance and surface quality also the final treatment by mechanical "action give. In practice, the maximum amount of abrasive grain "is included et via 7ü vol .-> i> and the minimum proportion at around 12; "j.

Abrasives based on alumina or silicon carbide, grain number Λό (approx. 0.35 mm), proved to be particularly useful for the production of grinding wheels according to the invention. When using alumina one prefers ■ · 6Q ^ S '"; $ " ■ abrasive grain with 31 »5 $ binder and with silicon carbide,'".: "03.8 % in 36.2 ρ binder. ■;. ■ .- ■ ·,.; .- ■ -. - ..-_ - ■: - "- .7 ■ '; ·· ■■ -> ^: ■■■: ■

A plienolic Earz'oulver "contains" ., ..- containing IC % hexamethylenetetramine in an amount of ,,., ... ,, vony;>8> 6 / i, as Iletallpulver vairde 57,?>% Serves as a binding agent Silver ü, 9 to l _t k ai. and another 3,6 ^ XaIk used as a filler.

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Instead of the abrasive grit specified above, you can also Use finer material e.g. grit number 100 (0.15 now).

Instead of the abrasive grit mentioned, you can also use Apply diamonds.

In the example given here, there is 15 volume # of silver in the bond and approx. 8 vol. # in the finished grinding wheel corresponding to approx. 18 wt.

Test rods ™ were used to determine the "grinding performance" 25xl00mm (ix ^ in.) Applied, current 230 A, voltage 2 V. A similarly structured grinding tool with 11 vol .- # silver shows a current of 100 A at 3 V, which is satisfactory. With 9 vol. Of silver, the conductivity is practically zero, namely less than 10 A at 1 to 4 V.

Other conventional phenolic resins can also be used. Inexpensive and widely available ones are preferred. Virtually any thermosetting moldable resin can be used as long as it does not cause any risk of attack on the silver.

The surprisingly high conductivity of the grinding wheels ι

not '

according to the invention is likely to be complete homogeneous distribution of the silver in the bond. Microscopic images of the finished grinding wheels showed that the silver, if it is initially homogeneously underlaid, to guide paths during the subsequent processing of the mixture segregates when 10 to 25 vol .- # organic in the mixture Binder are present and the grain size of the silver is less than 10 / U amounts to.

Claims

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Claims (7)

Claims 1. Organically bonded electrically conductive grinding media for electrochemical grinding, containing abrasive grain and lietallpulver in a thermoset resin, geke η η- is characterized by 10 to 25 Gew .- ^ finely divided silver. 2. Sole body according to claim 1, characterized in that the resin is a phenolic resin. 3. The method according to claim 1 or 2, characterized g e Ic e η η shows that the abrasive grain 12 to? 0 vol .- ^ matters. ^L K method according to claims 1 to 3, characterized in that the abrasive grain is diamond, aluminum oxide or silicon carbide. 5. Method zur'Herstellung of the abrasive articles according to claim 1 to k, characterized in that ic: up to 25 vol. Mixes silver with a grain size below ICyU, adds abrasive grain to the mixture and forms and hardens in the usual way. 6. The method according to claim 5, characterized in that the binder is a phenol-aldehyde condensation product and hexamethylenetetramine used as hardener. 9 09 826/0899 BATH ORIGINAL 1 β π 5? 9 η 7. The method according to claim 6, characterized in that g e k e η η - hardens up to 150 to 160 ° C i c h η e t that one cures at 150 to 160.degree. 909826/0899