CH589917A5

CH589917A5 - Graphite mouldings contg. fine metal powder - with optimum electrical conductivity and abrasion resistance, suitable for brushes

Info

Publication number: CH589917A5
Application number: CH647374A
Authority: CH
Original assignee: Lonza Ag
Priority date: 1974-05-13
Filing date: 1974-05-13
Publication date: 1977-07-29

Abstract

Electrically conducting mouldings with isotropic properties are made from graphite and >=1 other conducting material. Graphite powder with grain size 400 mu is suspended in a carrier in which a carbonisable binder is also dissolved or dispersed; the suspension is spray dried to obtain spheroids, fed into a fluisided bed drier for coating with at least one layer of conducting material. The conducting material is suspended in a carrier contg. a carbonisable binder in soln. or dispersion, where 0.1-20% binder is used w.r.t. the conducting material, the suspension being fed into the drier. The coated and dried graphite spheroids are pressed into mouldings and subjected to heat treatment. The mouldings are used for electric contacts, e.g. Cu brushes contg. a large amt. of graphite and used in motors for domestic appliances, razors, or starter motors. As compared with conventional brushes, the graphite content is higher so abrasion resistance is better, but good electrical conductivity is attained, even with only 40% Cu. Silver can be used instead of Cu, and also other metals, e.g. Fe, Co, Ni, Au, Al.

Description

  

  
 



   Die Erfindung betrifft ein Verfahren zur Herstellung von Formkörpern mit elektrischer Leitfähigkeit und vorwiegend isotropen Eigenschaften aus Graphit und mindestens einem weiteren Material mit elektrischer Leitfähigkeit.



   Es ist bekannt, Materialien für elektrischen Kontakt so herzustellen, dass man geschmolzenes Metall, vorzugsweise Kupfer, in die Poren von Kohlematerial einbringt (US-Pat.



  1 053 881, belg. Pat. 446 346). Ferner ist es bekannt, porösen Graphit auf Temperaturen bis   700"    C in nichtoxydierender Atmosphäre zu erhitzen und den Graphitkörper mit Dämpfen von Gruppe VI-B-Metall-Hexacarbonylen zu behandeln, wobei die Metallverbindung in die Poren des Graphits dringt    (US-Pat. 3    157 531).



   Es ist ferner bekannt, verdichtetes Graphitpulver mit im wesentlichen kugeligem Korn mit Metallpulver zu vermischen und damit Metallkohlebürsten herzustellen. Dazu ist es notwendig, zuerst den Graphit in Tablettenform zu bringen und dann wieder auf kleinere Korngrössen herunterzumahlen. Der notwendige Anteil an Metallpulver ist mit rund 60% relativ hoch.



   Die bekannten Verfahren haben den Nachteil, dass viel Metall im Verhältnis zum Graphit angewendet werden muss.



  Zudem sind für die Metallschmelzen oder die Zersetzung von Metallsalzen in die Metalle hohe Temperaturen erforderlich, oder der Graphit bedarf einer umfangreichen Aufarbeitung.



  Bei der Herstellung von Formkörpern neigen solche Metall Graphitgemische zur Entmischung.



   Ziel der Erfindung ist ein Verfahren zur einfachen Herstellung von Formkörpern mit elektrischer Leitfähigkeit, isotropen Eigenschaften und zusammenhängender Metallmatrix, wobei die Mengenverhältnisse zwischen Graphit und den weiteren Materialien in weiten Grenzen variiert werden können, ohne dass die vorteilhaften Eigenschaften verändert werden.

  Erfindungsgemäss wird das dadurch erreicht, dass man eine Aufschlämmung von Graphitpulver, mit einer Korngrösse von kleiner als   400,um,    in einem Trägermittel, in dem ein verkokbares Bindemittel gelöst oder dispergiert ist, einer Sprühtrocknung unterwirft, das dabei gewonnene, kugelige Graphitmaterial in einen Fliessbetttrockner führt und dabei mit mindestens einer Schicht eines elektrisch leitenden Materials beschichtet, wobei das elektrisch leitende Material als Aufschlämmung in einem Trägermittel, in dem ein verkokbares Bindemittel in Mengen von 0,1 bis 20%, bezogen auf die Menge elektrisch leitenden Materials, gelöst oder dispergiert ist, auf das kugelige Graphitmaterial aufgebracht und getrocknet wird und das beschichtete kugelige Graphitmaterial zu Formkörpern verarbeitet und die Formkörper anschliessend einer Wärmebehandlung unterzieht.



   Das Verfahren wird so ausgeführt, dass man eine Aufschlämmung herstellt aus 30 bis   75 Wo    natürlichem und/oder synthetischem Graphit, mit einer Korngrösse von kleiner als   400,zum,    vorzugsweise 0,1 bis   300,um,    in einem Trägermittel, in dem ein verkokbares Bindemittel in Mengen von kleiner als   40%,    vorzugsweise 5 bis 20%, bezogen auf die Menge Trägermittel, gelöst oder dispergiert ist. Beispielsweise kann als Bindemittel Phenolformaldehydharz oder Steinkohlenteerpech verwendet werden. Geeignete Trägermittel sind Wasser, Alkohole, Ketone, aliphatische oder aromatische Kohlenwasserstoffe, vorzugsweise Wasser, Methanol, Äthanol, Aceton, Benzol, Benzine. Die Aufschlämmung wird in eine Sprühtrocknungsapparatur eingespeist.

  Die Trocknungstemperatur liegt zwischen 150 und   450"    C. Aus der Sprühtrocknungsapparatur wird ein Graphitmaterial mit einer kugeligen Form und einer Korngrösse von 40 bis 800 um ausgetragen. Das Graphitmaterial ist   freifliessend    und die einzelnen Körner sind ausgesprochen formstabil. In einer Fliessbetttrockenvorrichtung wird dem Graphitmaterial mindestens eine Schicht eines elektrisch leitenden Materials aufgesprüht. Dazu wird ein elektrisch leitendes Material in eine Mischung, bestehend aus einem der oben genannten Trägermittel und einem darin gelösten oder dispergierten, verkokbaren Bindemittel, beispielsweise Phenolformaldehydharz oder Steinkohlenteerpech, eingebracht und durch Rühren eine Aufschlämmung hergestellt.



  Das elektrisch leitende Material weist zweckmässig eine Korngrösse von bis zu   100,um    auf. Diese Aufschlämmung wird in einen Fliessbetttrockner eingesprüht. Das elektrisch leitende Material bleibt in einer gleichmässig dicken Schicht auf dem kugelförmigen Graphitmaterial haften. Die Temperatur im
Fliessbetttrockner richtet sich nach dem verwendeten Trägerund Bindemittel. Es können nötigenfalls auch nacheinander mehrere Schichten elektrisch leitendes Material aufgesprüht werden.



   Als elektrisch leitendes Material können alle an sich bekannten Materialien angewendet werden, beispielsweise Kupfer, Gold, Silber, Eisen, Kobalt, Nickel, Zink, Platin, Blei, Aluminium, deren Gemische, Verbindungen oder Legierungen
Die Menge elektrisch leitenden Materials, bezogen auf die
Menge Graphitmaterial, kann in weiten Grenzen variiert werden und richtet sich nach dem Einsatzzweck und den gewünschten Eigenschaften des Endproduktes. Das beschichtete Graphitmaterial, das aus dem Fliessbetttrockner ausgetra gen werden kann, ist wiederum kugelförmig und freifliessend.



  Das Produkt wird in bekannter Weise zu den gewünschten Formkörpern gepresst. Die mit dem erfindungsgemässen
Material hergestellten Formkörper sind sehr stabil und können nach dem Verpressen einer Wärmebehandlung unterzogen werden.



   Nach dem erfindungsgemässen Verfahren können bei spielsweise Kupferbürsten für Elektromotoren hergestellt werden, die einen hohen Graphitgehalt aufweisen und bei guter elektrischer Leitfähigkeit und geringer Abnützung nur relativ wenig Kupfer benötigen, da durch die erfindungsgemässe Herstellung eine zusammenhängende Metallmatrix er halten wird. Formkörper, bei denen die Beschichtung des Graphitmaterials mit Kupfer oder Silber vorgenommen wurde, sind geeignet für Elektromotoren in Haushaltgeräten, Elektrorasierer, Bürsten für Startermotoren.



   Beispiel
Eine Dispersion, bestehend aus 40% Graphit mit einer durchschnittlichen Korngrösse von   100 um,    10% Phenolformaldehydharz und   50%    Wasser, wurde bei   350"    C einer Sprühtrocknung unterworfen. Es resultierte ein kugeliges Graphitmaterial, das in einen Fliessbetttrockner eingeführt wurde. Im Fliessbetttrockner wurde auf das Graphitmaterial eine Aufschlämmung, bestehend aus 93 % Äthanol, 2% Phenolformaldehydharz und   5 %    Kupferpulver mit einer Korngrösse von durchschnittlich   25 um,    aufgesprüht und bei   600 C    getrocknet.

  Das beschichtete kugelige Graphitmaterial war   freifliessend    und formstabil und wurde bei Drücken von rund 2,0 bis 3,0 t/cm2 gepresst und während 32 Stunden auf   250     C erhitzt und anschliessend bei   800"    C und einem Druck von 10 Torr während 20 Stunden gesintert. Durch die guten Fülleigenschaften und die gute Pressbarkeit des Materials war die Herstellung der Formkörper problemlos. Die Formkörper weisen einen spezifischen elektrischen Widerstand von 2,0 Q mm2/m bei einem Kupfergehalt von   40 %    auf. Bei Vergleichsmustern, hergestellt nach bekannten Methoden, mussten, um die gleichen Werte zu erreichen, rund 70% Kupfer aufgewendet werden, Bei den erfindungsgemässen Formkörpern waren aber die Abriebeigenschaften entsprechend dem hohen Graphitgehalt wesentlich besser.



   PATENTANSPRUCH



   Verfahren zur Herstellung von Formkörpern mit elektrischer Leitfähigkeit und vorwiegend isotropen Eigenschaften 

**WARNUNG** Ende DESC Feld konnte Anfang CLMS uberlappen**.



   



  
 



   The invention relates to a method for the production of shaped bodies with electrical conductivity and predominantly isotropic properties from graphite and at least one further material with electrical conductivity.



   It is known to manufacture materials for electrical contact by introducing molten metal, preferably copper, into the pores of carbon material (US Pat.



  1 053 881, Belgian Pat. 446 346). It is also known to heat porous graphite to temperatures of up to 700 "C in a non-oxidizing atmosphere and to treat the graphite body with vapors from Group VI-B metal hexacarbonyls, the metal compound penetrating the pores of the graphite (US Pat. 3 157 531).



   It is also known to mix compacted graphite powder with a substantially spherical grain with metal powder and thus to produce metal carbon brushes. To do this, it is necessary to first bring the graphite into tablet form and then grind it back down to smaller grain sizes. The necessary proportion of metal powder is relatively high at around 60%.



   The known methods have the disadvantage that a lot of metal must be used in relation to the graphite.



  In addition, high temperatures are required for the metal melts or the decomposition of metal salts into the metals, or the graphite requires extensive processing.



  In the production of moldings, such metal-graphite mixtures tend to separate.



   The aim of the invention is a method for the simple production of molded bodies with electrical conductivity, isotropic properties and a cohesive metal matrix, wherein the quantitative ratios between graphite and the other materials can be varied within wide limits without changing the advantageous properties.

  According to the invention, this is achieved by spray drying a slurry of graphite powder, with a grain size of less than 400 μm, in a carrier in which a coking binder is dissolved or dispersed, and then subjecting the spherical graphite material obtained to a fluidized bed dryer and coated with at least one layer of an electrically conductive material, the electrically conductive material being dissolved or dispersed as a slurry in a carrier in which a coking binder in amounts of 0.1 to 20%, based on the amount of electrically conductive material is, is applied to the spherical graphite material and dried and the coated spherical graphite material is processed into shaped bodies and the shaped bodies are then subjected to a heat treatment.



   The process is carried out in such a way that a slurry is prepared from 30 to 75 W of natural and / or synthetic graphite, with a grain size of less than 400, preferably 0.1 to 300 .mu.m, in a carrier in which a coking Binder in amounts of less than 40%, preferably 5 to 20%, based on the amount of carrier, dissolved or dispersed. For example, phenol-formaldehyde resin or coal tar pitch can be used as a binder. Suitable carriers are water, alcohols, ketones, aliphatic or aromatic hydrocarbons, preferably water, methanol, ethanol, acetone, benzene, and gasoline. The slurry is fed into a spray drying apparatus.

  The drying temperature is between 150 and 450 "C. A graphite material with a spherical shape and a grain size of 40 to 800 μm is discharged from the spray drying apparatus. The graphite material is free-flowing and the individual grains are extremely dimensionally stable. In a fluid bed drying device, at least one For this purpose, an electrically conductive material is introduced into a mixture consisting of one of the above-mentioned carriers and a coking binder dissolved or dispersed therein, for example phenol-formaldehyde resin or coal tar pitch, and a slurry is produced by stirring.



  The electrically conductive material expediently has a grain size of up to 100 μm. This slurry is sprayed into a fluid bed dryer. The electrically conductive material adheres to the spherical graphite material in a uniformly thick layer. The temperature in
Fluid bed dryer depends on the carrier and binder used. If necessary, several layers of electrically conductive material can be sprayed on one after the other.



   All materials known per se can be used as the electrically conductive material, for example copper, gold, silver, iron, cobalt, nickel, zinc, platinum, lead, aluminum, their mixtures, compounds or alloys
The amount of electrically conductive material based on the
Amount of graphite material can be varied within wide limits and depends on the intended use and the desired properties of the end product. The coated graphite material that can be discharged from the fluid bed dryer is again spherical and free-flowing.



  The product is pressed in a known manner into the desired shaped bodies. The with the inventive
Moldings made from the material are very stable and can be subjected to a heat treatment after pressing.



   According to the inventive method, for example, copper brushes for electric motors can be produced which have a high graphite content and require relatively little copper with good electrical conductivity and little wear, since a cohesive metal matrix is obtained through the inventive production. Shaped bodies in which the graphite material has been coated with copper or silver are suitable for electric motors in household appliances, electric razors, brushes for starter motors.



   example
A dispersion consisting of 40% graphite with an average grain size of 100 μm, 10% phenol-formaldehyde resin and 50% water was subjected to spray drying at 350 ° C. The result was a spherical graphite material which was introduced into a fluidized bed dryer the graphite material is a slurry consisting of 93% ethanol, 2% phenol-formaldehyde resin and 5% copper powder with an average particle size of 25 μm, sprayed on and dried at 600.degree.

  The coated spherical graphite material was free-flowing and dimensionally stable and was pressed at pressures of around 2.0 to 3.0 t / cm2 and heated to 250 ° C. for 32 hours and then sintered at 800 ° C. and a pressure of 10 Torr for 20 hours. Due to the good filling properties and the good compressibility of the material, the production of the moldings was problem-free. The moldings have a specific electrical resistance of 2.0 Ωmm2 / m with a copper content of 40%. In order to achieve the same values, around 70% copper is used. In the case of the molded bodies according to the invention, however, the abrasion properties were significantly better, corresponding to the high graphite content.



   PATENT CLAIM



   Process for the production of moldings with electrical conductivity and predominantly isotropic properties

** WARNING ** End of DESC field could overlap beginning of CLMS **.

Claims

** WARNING ** Beginning of CLMS field could overlap end of DESC **.

The invention relates to a method for the production of shaped bodies with electrical conductivity and predominantly isotropic properties from graphite and at least one further material with electrical conductivity.

It is known to manufacture materials for electrical contact by introducing molten metal, preferably copper, into the pores of carbon material (US Pat.

1 053 881, Belgian Pat. 446 346). It is also known to heat porous graphite to temperatures of up to 700 "C in a non-oxidizing atmosphere and to treat the graphite body with vapors from Group VI-B metal hexacarbonyls, the metal compound penetrating the pores of the graphite (US Pat. 3 157 531).

It is also known to mix compacted graphite powder with a substantially spherical grain with metal powder and thus to produce metal carbon brushes. To do this, it is necessary to first bring the graphite into tablet form and then grind it back down to smaller grain sizes. The necessary proportion of metal powder is relatively high at around 60%.

The known methods have the disadvantage that a lot of metal must be used in relation to the graphite.

In addition, high temperatures are required for the metal melts or the decomposition of metal salts into the metals, or the graphite requires extensive processing.

In the production of moldings, such metal-graphite mixtures tend to separate.

The aim of the invention is a method for the simple production of molded bodies with electrical conductivity, isotropic properties and a cohesive metal matrix, wherein the quantitative ratios between graphite and the other materials can be varied within wide limits without changing the advantageous properties.

According to the invention, this is achieved by spray drying a slurry of graphite powder, with a grain size of less than 400 μm, in a carrier in which a coking binder is dissolved or dispersed, and then subjecting the spherical graphite material obtained to a fluidized bed dryer and coated with at least one layer of an electrically conductive material, the electrically conductive material being dissolved or dispersed as a slurry in a carrier in which a coking binder in amounts of 0.1 to 20%, based on the amount of electrically conductive material is, is applied to the spherical graphite material and dried and the coated spherical graphite material is processed into shaped bodies and the shaped bodies are then subjected to a heat treatment.

The process is carried out in such a way that a slurry is prepared from 30 to 75 W of natural and / or synthetic graphite, with a grain size of less than 400, preferably 0.1 to 300 .mu.m, in a carrier in which a coking Binder in amounts of less than 40%, preferably 5 to 20%, based on the amount of carrier, dissolved or dispersed. For example, phenol-formaldehyde resin or coal tar pitch can be used as a binder. Suitable carriers are water, alcohols, ketones, aliphatic or aromatic hydrocarbons, preferably water, methanol, ethanol, acetone, benzene, and gasoline. The slurry is fed into a spray drying apparatus.

The drying temperature is between 150 and 450 "C. A graphite material with a spherical shape and a grain size of 40 to 800 μm is discharged from the spray drying apparatus. The graphite material is free-flowing and the individual grains are extremely dimensionally stable. In a fluid bed drying device, at least one For this purpose, an electrically conductive material is introduced into a mixture consisting of one of the above-mentioned carriers and a coking binder dissolved or dispersed therein, for example phenol-formaldehyde resin or coal tar pitch, and a slurry is produced by stirring.

The electrically conductive material expediently has a grain size of up to 100 μm. This slurry is sprayed into a fluid bed dryer. The electrically conductive material adheres to the spherical graphite material in a uniformly thick layer. The temperature in Fluid bed dryer depends on the carrier and binder used. If necessary, several layers of electrically conductive material can be sprayed on one after the other.

All materials known per se can be used as the electrically conductive material, for example copper, gold, silver, iron, cobalt, nickel, zinc, platinum, lead, aluminum, their mixtures, compounds or alloys The amount of electrically conductive material based on the Amount of graphite material can be varied within wide limits and depends on the intended use and the desired properties of the end product. The coated graphite material that can be discharged from the fluid bed dryer is again spherical and free-flowing.

The product is pressed in a known manner into the desired shaped bodies. The with the inventive Moldings made from the material are very stable and can be subjected to a heat treatment after pressing.

According to the inventive method, for example, copper brushes for electric motors can be produced which have a high graphite content and require relatively little copper with good electrical conductivity and little wear, since a cohesive metal matrix is obtained through the inventive production. Shaped bodies in which the graphite material has been coated with copper or silver are suitable for electric motors in household appliances, electric razors, brushes for starter motors.

example A dispersion consisting of 40% graphite with an average grain size of 100 μm, 10% phenol-formaldehyde resin and 50% water was subjected to spray drying at 350 ° C. The result was a spherical graphite material which was introduced into a fluidized bed dryer the graphite material is a slurry consisting of 93% ethanol, 2% phenol-formaldehyde resin and 5% copper powder with an average particle size of 25 μm, sprayed on and dried at 600.degree.

The coated spherical graphite material was free-flowing and dimensionally stable and was pressed at pressures of around 2.0 to 3.0 t / cm2 and heated to 250 ° C. for 32 hours and then sintered at 800 ° C. and a pressure of 10 Torr for 20 hours. Due to the good filling properties and the good compressibility of the material, the production of the moldings was problem-free. The moldings have a specific electrical resistance of 2.0 Qmm2 / m with a copper content of 40%. In the case of comparison samples, produced according to known methods, In order to achieve the same values, around 70% copper is used. In the case of the molded bodies according to the invention, however, the abrasion properties were significantly better, corresponding to the high graphite content.

PATENT CLAIM

Process for the production of moldings with electrical conductivity and predominantly isotropic properties from graphite and at least one other material with electrical conductivity, characterized in that a slurry of graphite powder, with a grain size of less than 400 .mu.m, is placed in a carrier in which a coking binder is dissolved or dispersed, subjected to spray drying, the spherical graphite material obtained thereby leads into a fluidized bed dryer and coated with at least one layer of an electrically conductive material, the electrically conductive material as a slurry in a carrier in which a cokable binder in quantities from 0.1 to 20%, based on the amount of electrically conductive material, is dissolved or dispersed,

is applied to the spherical graphite material and dried and the coated spherical graphite material is processed into shaped bodies and the shaped bodies are then subjected to a heat treatment.